Documentation corrections

Corrected some spelling errors and added / correceted some references
Handlingh of -- by \c and <code> results in - adjusted documentation

Adjusted documentation so that -- in \c and <code> are shown as -- by placing the parts in ` (backtick)
Use hook arrow for hyphens in symbol names in the LaTeX output.
Fixed potential crash caused by overloading the variadic warn function
Merge branch 'master' of github.com:doxygen/doxygen
Merge pull request #99 from CraigNoble/master

Fix to VHDL scanner.
Merge pull request #89 from albert-github/feature/docu_update

Documentation corrections