* add base ngraphcpp docs theme

* add base ngraphcpp docs theme and doc contributor README

* Add proper chars for tm and r symbols in main project sidebar

* nevermind that last commit

* added separate sphinx_doc and doxygen_doc targets to the contrib/docker/Makefile to build html docs for PR #377

* explicitly marked non-ascii string as unicode for sphinx conf.py

* updated the sphinx version using pip install in Dockerfile.ngraph_cpp

added a make target to build the docs to the contrib/docker/Makefile

* avoid upgrade pip message during build

* Initial pass as supporting ngraph_dist builds with both gcc and clang.  Includes deprecated targets to support Jenkins CI with old feature and development branches that may not have these changes.

* Added build_all, check_all, and install_all targets

* Broke build and check steps into separate make sections.  Each step already generated its own log.

* Updated README.md

* Fixed a bug in the docker build context, which was overly general and included the build directories.  This caused a loop where the docker images rebuilt into multi-gigabyte images after testing was run (yikes).  New context is the contrib/docker directory, which is tiny.  No more image rebuilds.

* Rename the docker image to be less generic, so that another tool doesn't accidentally use the same name

* Change compatibility target "make check_cpu" to run "make check_all", so that all builds are done.

* Add a conversion step to change the test-suite names for all unit tests, to include an indicator for what compiler was used for the builds (_gcc vs _clang).

* Unfortunately, modifying the test-suite name with compiler suffix did not show in Jenkins test results.  Now modifying classname instead.

* Switch builds to be RelWithDebInfo, which turns on optimization and includes debug symbols.  Remove verbose output when creating tarball, to reduce log fluff.

Add GTEST_OUTPUT environment variable definition, to generate an xml report from the unit-testing (written in Google Test).

* Refactored to run builds as user, not as root.  Added make install.  Added parallel build.  Expanded make clean to remove BUILD directory.  Moved log generation to makefile, so Jenkins job can let make do all of the work.

* Changes/fixes to address code review.  Mainly adding double-quotes around variables and using $(...) expansion where appropriate (and semantically identical to back-quotes).

* Add double-quotes for variable expansion safety.  Write error message in run_as_user.sh to stderr.

* Remove chown_files.sh, made obsolete by running as user inside docker container.  Add set -e and set -u to run_as_user.sh, for further protection.

Moved all apt-get install commands into same RUN line as apt-get update.  There is a subtle timebomb if apt-get update is performed in a separate RUN line, due to how docker layers work. (#179)

* Forces CI to use clang-3.9

Changes to allow build (in docker run) to run as the user, not root, so BUILD directory is easily removable.

Added "make check_cpu" target.  Removed unused definitions from Makefile.  Added chown_files.sh to ngraph_cpp_cpu image, instead of creating new image.

Add a couple scripts from ngraph/contrib/docker.  chown_files.sh solves a file permissions problem involving mounted directories in docker images.