various updates
Reorganized changes/release files, added Clawpack 5 to top of page
improving installation instructions
updated instructions for running first example
merged page width changes and added Clawpack 5 to top line
Streamline installation instructions.
Fix typos and link to PyClaw changelog.
Fix underline and put simple install first.
Fix typos, h/t @mandli.
Merge pull request #29 from ketch/updates2

Revision of installation instructions