Introduce CharSequenceAssert

This is required to support StringBuffer and StringBuilder assertions.
Issue #21
Fix generics
Fixes #69 : typo in contribution guide
[maven-release-plugin] prepare release assertj-core-1.2.0
[maven-release-plugin] prepare for next development iteration
Release 1.2.0 doc
Better latest news section in README.md
Fix contributors section (shame on me for the error on William last name)