Reintroduced implementation of Difbuffer used moose objects that have
been since rewritten and renamed.  Change used moose objects to
current version.

Change process_0 to proc, to match other classes which need to be
driven by ticks.

π is defined as a constant in the headers, no need to create a
variable. Also constify some other variables. No functional change.

New getters and setters are added.

Fixed grammar and typo.

Added links to install/index.rst file; and also to online file link.

Fixed typos.

removed url. URL is listed on the project page.

Added clang compiler also to travis.

Update index.rst

formatting.

known_issues and release notes.

documentation.