Add uninstall target (fix #104)

Adds an uninstall target, so that 'make uninstall' will remove
all installed files, provided that the build folder is retained.
It will not remove any folders that were created during
installation.
Fix uninstall script to handle spaces in file names

Fixed a few cmake syntax problems and added quotation marks
to remove command to handle spaces in file names.
Merge pull request #106 from scpeters/issue_104_uninstall

Add uninstall target (fix #104). Works for files but leaves empty directories.