updated NuPIC installation readme
updated readme w/ info for contributors
Merge pull request #1582 from BoltzmannBrain/new_readme

updated NuPIC installation readme
fixed variable name in spatial_pooler.py comments
Merge pull request #1603 from BoltzmannBrain/sp_typo

spatial_pooler.py comments typo
Updates nupic.core to 64f7abb2903120a253d634d8d15dcbca4ca8dca7.
Merge pull request #1607 from numenta-ci/core-update-sha

Updates nupic.core to latest built SHA.
Merge branch 'master' of github.com:numenta/nupic into build_extensions

Conflicts:
	.nupic_modules