Makefile enhancements.

Primarily, this allows for custom build flags for the compiler and linker
to be passed in externally. There's also a bit of cleanup to make it simpler
to add more targets later on, like in the upcoming manual page patch.
Adding manual page.

Even small utilities benefit from documentation!

In addition to the manpage itself, a target is added to the makefile to
allow for generating and installing a compressed version.
Merge pull request #12 from felixc/makefile-and-manpage

Makefile enhancements and a new manual page