Use CLAW variable for pyclaw gallery path, if available.
Merge pull request #52 from ketch/pyclaw_gallery_path

Use CLAW variable for pyclaw gallery path, if available.
update version in installing
Merge remote-tracking branch 'origin/master' into 5.1.0
Trying to fix reversion of docs to 5.0.0 in
https://github.com/clawpack/clawpack.github.com/commit/7e6bc9fa54fc9e356f878c7f618cf0142639d22b

* origin/master:
  Use CLAW variable for pyclaw gallery path, if available.