Programmable filter can add dimensions to context

Using one or more `add_dimension` options on a programmable filter will
instruct the filter to add those dimensions to the primary
PointContext. This way, the programmable filter can set dimensions that
might be not present on the PointContext at first.
add random kernel

* uniform distribution (user-defined bounds)
* normal distribution (user-defined mean and standard deviation)
Stick embedded BPF ULEM files into metadata.
Merge pull request #452 from PDAL/bpfmeta

Stick embedded BPF ULEM files into metadata.
Merge pull request #450 from chambbj/random-ctx

add random kernel
Merge pull request #447 from gadomski/programmable-add-dimension

Programmable filter can add dimensions to context
Remove leftover embedded boost cruft

Removes IsEmbeddedBoost() and calls, as well as embedded boost check in
test/unit/CMakeLists.txt.
Include info in debug output
Fix test value
BPF spatial reference in metadata.
PointContext -> PointContextRef
Merge branch 'master' of https://github.com/PDAL/PDAL into ptctxref
Merge pull request #455 from PDAL/ptctxref

Ptctxref
Merge pull request #453 from gadomski/remove-embedded-boost-cruft

Remove leftover embedded boost cruft
Merge branch 'master' into rxp-driver