changes for release 5.0.1
for 5.0.1rc-alpha, not yet releasing
updated changes to include geoclaw/new_dtopo changes
changed 5.0.1 to 5.1.0 since we decided this would be a more major release
change version to 5.1.0 in conf.py
added dt_max_dtopo descriptions
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.
Merge pull request #54 from rjleveque/5.1.0

5.1.0