Add CONTRIBUTING.md

A CONTRIBUTING file can be useful for guiding new developers when they
are submitting changes, and Github supports
(https://github.com/blog/1184-contributing-guidelines) integration of
these CONTRIBUTING files into the pull request user interface.

This patch adds a basic CONTRIBUTING file.
Merge pull request #323 from gadomski/contributing

Add CONTRIBUTING.md
step back to allowing boost 1.52, force a re-find_package of boost when PCL is enabled (its CMake mucks up the components
point to PCL
put bakc c++0x flag for gcc
implement an enabled static flag for Stage:: #325
Merge pull request #325 from PDAL/issues/325-stage-enabled-status

pdal info --drivers should tell you whether or not a driver is enabled
Add default statement to fix busted GCC implementation.
clean up some cast warnings that gcc 4.8 found
ignore ./lib directory
don't link to ourselves for libpdalcpp.so
update my config
use RPATH on OSX by default now
Merge pull request #327 from PDAL/issues/326-missing-case

Add default statement to fix busted GCC implementation.
Add a sbet writer

This writer can create sbet files, which store IMU data. Since the sbet
format is pretty dumb (just a struct), this writer is pretty dumb as
well.
Update doxygen.conf

This update was done by running `doxygen -u doc/doxygen/doxygen.conf`.
Without this patch, doxygen 1.8.4 produces warnings when run with our
configuration file.  For example:

> Warning: Tag `SYMBOL_CACHE_SIZE' at line 323 of file doc/doxygen/doxygen.conf has become obsolete.

This patch removes those warnings.
Remove m_pointCountType and references

Per discussion in #328, pointCountType is not and will mostly likely not
be used. This patch removes the member variable from Stage and all
references to that variable and its associated methods.

Closes #329.
add --detail to 'pdal delta' doc
Fix some warnings during doc building

sphinx 1.2.1 was generating warnings in the following files, and this
patch fixes some of those warnings. Some warnings still exist:

- "pdal_logo.png does not exist": this is a sphinx bug that has been fixed in
  https://bitbucket.org/birkenfeld/sphinx/issue/1352/copying-html_logo-file-over-improperly

- "Ignoring duplicate domain reference...": I haven't been able to track
  down the source of this warning yet.

- "doc/index.txt: document isn't included in any toctree": this seems to
  be an intentional design decision for the website, so I didn't touch
  it.
Merge pull request #331 from gadomski/issue/doc-warnings

Fix some documentation warnings