Fix documentation links to other packages

R CMD check with R-devel r87224-ish NOTEs:

  Found the following Rd file(s) with Rd \link{} targets missing package
  anchors:
    as.xts.Rd: zoo
    diff.xts.Rd: lag.zoo
    merge.xts.Rd: merge.zoo
    print.xts.Rd: coredata
    split.xts.Rd: split.zoo, aggregate.zoo
    tclass.Rd: index
    tformat.Rd: index
    tzone.Rd: index
    xts.Rd: index
  Please provide package anchors for all Rd \link{} targets not in the
  package itself and the base packages.

R/lag.xts.R

@@ -52,7 +52,7 @@ lagts.xts <- function(x, k=1, na.pad=TRUE, ...) {
 #' 
 #' The primary motivation for these methods was to take advantage of a faster
 #' C-level implementation. Another motivation was to make `lag()` behave using
-#' standard sign for `k`. Both [`lag.zoo()`] and [`lag.default()`] require a
+#' standard sign for `k`. Both [zoo's lag() method][zoo::lag.zoo] and [`lag.default()`] require a
 #' *negative* value for `k` in order to shift a series backward. So `k = 1`,
 #' shifts the series *forward* one observation. This is especially confusing
 #' because `k = 1` is the default for those functions. When `x` is an xts

R/merge.R

@@ -23,7 +23,7 @@
 #' 
 #' Perform merge operations on xts objects by time index.
 #' 
-#' This xts method is compatible with [`merge.zoo()`] but implemented almost
+#' This xts method is compatible with [zoo's merge() method][zoo::merge.zoo] but implemented almost
 #' entirely in C-level code for efficiency.
 #' 
 #' The function can perform all common database join operations along the time

R/print.R

@@ -24,7 +24,7 @@
 #' Method for printing an extensible time-series object.
 #' 
 #' @param x An xts object.
-#' @param fmt Passed to [`coredata()`] to format the time index.
+#' @param fmt Passed to [`coredata()`][zoo::coredata] to format the time index.
 #' @param \dots Arguments passed to other methods.
 #' @param show.rows The number of first and last rows to print if the number of
 #'   rows is truncated (default 10, or `getOption("xts.print.show.rows")`).

R/split.R

@@ -29,7 +29,7 @@
 #' [`endpoints()`] is used to find the start and end of each period (or
 #' k-periods). See that function for valid arguments.
 #' 
-#' The inputs are passed to [`split.zoo()`] when `f` is not a character vector.
+#' The inputs are passed to [`split.zoo()`][zoo::split.zoo] when `f` is not a character vector.
 #' 
 #' @param x An xts object.
 #' @param f A character vector describing the period to split by.
@@ -39,12 +39,13 @@
 #' 
 #' @return A list of xts objects.
 #' 
-#' @note [`aggregate.zoo()`] is more flexible, though not as fast for xts
-#' objects.
+#' @note [`aggregate.zoo()`][zoo::aggregate.zoo] is more flexible, though not
+#' as fast for xts objects.
 #' 
 #' @author Jeffrey A. Ryan
 #' 
-#' @seealso [`endpoints()`], [`split.zoo()`][zoo::zoo], [`aggregate.zoo()`][zoo::zoo]
+#' @seealso [`endpoints()`], [`split.zoo()`][zoo::split.zoo],
+#' [`aggregate.zoo()`][zoo::aggregate.zoo]
 #' 
 #' @keywords utilities
 #' @examples

R/tclass.R

@@ -51,7 +51,7 @@
 #' 
 #' @author Jeffrey A. Ryan
 #' 
-#' @seealso [`index()`] has more information on the xts index, [`tformat()`]
+#' @seealso [`index()`][xts::index.xts] has more information on the xts index, [`tformat()`]
 #' details how the index values are formatted when printed, and [`tzone()`]
 #' has more information about the index timezone settings.
 #' 

R/tformat.R

@@ -47,7 +47,7 @@
 #' 
 #' @author Jeffrey A. Ryan
 #' 
-#' @seealso [`index()`] has more information on the xts index, [`tclass()`]
+#' @seealso [`index()`][xts::index.xts] has more information on the xts index, [`tclass()`]
 #' details how \pkg{xts} handles the class of the index, [`tzone()`] has more
 #' information about the index timezone settings.
 #' 

R/tzone.R

@@ -57,7 +57,7 @@ indexTZ <- function(x, ...)
 #' 
 #' @author Jeffrey A. Ryan
 #' 
-#' @seealso [`index()`] has more information on the xts index, [`tformat()`]
+#' @seealso [`index()`][xts::index.xts] has more information on the xts index, [`tformat()`]
 #' describes how the index values are formatted when printed, and [`tclass()`]
 #' provides details how \pkg{xts} handles the class of the index.
 #' 

R/xts.R

@@ -129,7 +129,7 @@
 #' 
 #' @author Jeffrey A. Ryan and Joshua M. Ulrich
 #' 
-#' @seealso [`as.xts()`], [`index()`], [`tclass()`], [`tformat()`], [`tzone()`],
+#' @seealso [`as.xts()`], [`index()`][xts::index.xts], [`tclass()`], [`tformat()`], [`tzone()`],
 #' [`xtsAttributes()`]
 #' 
 #' @references \pkg{zoo}
@@ -413,7 +413,7 @@ function(x) {
 #' 
 #' `as.xts()` can convert objects of the following classes into an xts object:
 #' object: [timeSeries][timeSeries::timeSeries], [ts], [matrix], [data.frame],
-#' and [zoo]. `xtsible()` safely checks whether an object can be converted to
+#' and [zoo][zoo::zoo]. `xtsible()` safely checks whether an object can be converted to
 #' an xts object.
 #' 
 #' Additional `name = value` pairs may be passed to the function to be added to