Added initial documentation

Added initial documentation for the core methods in spatial_pooler.hpp
Removing obsolete .gitignore lines
Removing reverence to pbworks and syncEverything
Merge pull request #581 from oxtopus/cleanup-gitignore

Removing obsolete .gitignore lines
Merge pull request #580 from subutai/cppsp_docstring

Added initial documentation
Renamed TIMER_TEST_MS as apr_sleep() operates on microseconds, not milliseconds.
Increasing TimerTest sleep time to 100ms since 100us precision might not be available on some systems.
Merge pull request #592 from csimons/timer

Improvements in TimerTest.cpp.
Removing nta dir with all C++.
Added nupic.core as local submodule at "nta".

This replaces the previously removed `nta` directory with the nupic.core
codebase and names it `nta` to replace the deleted code.
Updated build script to refresh core submodule...

before building.
Added cleanup of nupic.core submodule after build.

The build leaves nupic.core submodule in an altered state because of the
files it dumps. This resets all submodules to initial state after
building.
Using secure URL for submodule
Cleanup build script re: submodule.

Trying to plan for different states. If a user removes the nta dir
submodule, this will put it back before initializing the submodule. Also
cleans up after build in a cleanup function.
Disabling Travis's submodule support.
Trying another URL for submodule.

Per
http://docs.travis-ci.com/user/build-configuration/#Use-Public-URLs-For-Submodules.
Fixing submodule url
Merge pull request #597 from rhyolight/core-submodule

Core submodule
Moved KNN Classifier regression test from trunk
Removed unnecessary test code