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.
Update overview for readers.
Add missing image.
Merge branch 'master' of https://github.com/PDAL/PDAL
Add tree depth query to QuadIndex.
Reorganize test data #441
Fix RST.
Remove chunk size

The --chunk-size app argument is no longer applicable. Removing it to
avoid future confusion.
add random kernel

* uniform distribution (user-defined bounds)
* normal distribution (user-defined mean and standard deviation)
Merge pull request #449 from gadomski/extract-chunk-size

Remove chunk size
output std::endl for each pt in --detail of 'pdal delta'
Update method used to get dimensions.
Fix dumping of dimensions from point context.
Merge pull request #451 from PDAL/bpfmeta

Fix dumping of dimensions from point context.
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.
BPF spatial reference in metadata.
PointContext -> PointContextRef