Add documentation for "disable_grep" configuration

Add some documentation about the new "disable_grep" option and its usage.
Merge pull request #87 from gnutix/master

Add documentation for "disable_grep" option
changes wording a bit
Added example for constants in Observe annotations
Merge pull request #140 from ruudk/patch-1

Added example for constants in Observe annotations
Merge branch 'master' into traitfix