Tokens bug fix

Tokens was not correctly building against the new boost tokenizor
version.

Hack it by renaming the include...
Bug fix to Commands

Previously the commands dispatcher only took function pointers. This was
an issue when trying to use the result of std::bind on a member
function. (.target returns null).

This can be worked around by additionally accepting std::function
objects when constructing the function
Enhance OSTools with file exists function

The OS library can now test for the existance of an object on the file
system
Enhance Commands with help text