3.0 - Initial work

[cpiker]

This merge provides the beginning of v3.0 stream handling, namely:

1. All existing das v2 unit-tests pass, new lib is almost 100% backwards compatible
2. Packet data are stored in much more versatile DasAry dynamic type and dynamic memory structures instead of coercing all values to doubles.
3. (Related to 2) TT2000 values are handled internally as integers and thus support nanosecond resolution over their entire legal range.
4. The non-namespace of the new stream format, "3.0/basic" is parsed into memory structures
5. DasVar internal indicies have a defined purpose. They can correspond to:
   a. String lengths, this way strings are treated as singletons
   b. Record geometric vector lengths, so that geometric vectors are treated as singletons.
6. The new stream object allows vector reference frames to be defined and referenced explicitly.
7. A significant new utility, das3_cdf is provided which serializes DasDs objects to ISTP CDF format.

Significant items that still need work on the road to v3.0, release-candidate-1 include:

1. DasBldr doesn't register callbacks to ingest v3.0 data, yet. (This is easy and required to support das2py, das2dlm etc.)
2. Legacy formats are not streamed into DasAry structures, yet.
3. The stream processors don't have v3.0 format versions, yet.
4. The pure xml format, *.d3x is not supported by DasIO, yet.