Release 1.2.0 (iiasa#213)

* Update release notes
* Update AUTHORS
* Update README
* Streamline setup.py, adding .dev0 version tag -- REMOVE BEFORE RELEASE
  - Also add long_description from README
* Purge rmessageix/.Rhistory
* Use IIASA ENE as author in setup.py
* Add summary/highlights to RELEASE_NOTES.md
* Set actual VERSION in setup.py for release

find version in setup.py the same way as in __init__.py (iiasa#128)

fix setup.py to work with conda

add note on pack_data