Some minor (non-functional) corrections to the documentation of Gomega.

There are speelin correcshuns, minor grammatical corrections has, and
occasional corrections to code snippets. Some code examples have
coding errors and some are just formatted unfortunately.
Merge pull request #57 from Zteve/minor_corrections

Some minor (non-functional) corrections to the documentation of Gomega.
Document HavePrefix and HaveSuffix matcher