Update genkeymap.c

Add a "shiftaltgr" section to the keymap generator, which should satisfy keyboard layouts such as km-0415
Update readme.txt
Update readme.txt

Corrected spelling and grammar.
Updated to reflect additional "shiftaltgr" section.
Merge pull request #105 from scarygliders/devel

Devel - please pull/merge these changes to the xrdp-genkeymap utility