Fixes bug#653.

* lispy-test.el
(lispy-simulate-key) (lispy-simulate-keys) (lispy-simulate-expect):
Added facilities to assert results after a given set of keypresses.
(lispy-read-unsafe-chars): added regression tests for bug#648.

Fixes bug#647.

Lispy would assume an implicit nil after the reader syntax, like this:

```emacs-lisp
(defun foo ()
  '
  (bar baz)
  ) ;; point here, press i to format
```

Gets this incorrect result:

```emacs-lisp
(defun foo ()
  '() (bar baz))
```

* lispy.el (lispy--delete-insignificant-sexps): allow removing sexps that are
implicitly-created by lispy, and serve no purpose in the real input and output
sexp other than formatting.  At the moment, just remove newline nodes.
(lispy--read-reader-syntax): helper function to avoid code duplication; replaces
a reader syntax RS, e.g., "`", plus its immediately-next sexp into an internal
representation with TAG.
(lispy--read): update handling of "#'", ",@", "'", "`", "," to make use of
`lispy--read-reader-syntax'.
(lispy--insert): fixed float and quasiquote handling (currently it calls
`(insert (caddr sxp))', which is incorrect because `insert' considers it a
character; float was not problematic because this code path was never triggered:
things like 1.2 have not been converted into `ly-raw float' constructs anyway.

* lispy-test.el (lispy-read-quote-newline): added 5 simple tests for each of the
addressed reader syntaxes.