improve spelling and clarity of readme

add license and readme in preparation for sharing

use exec by default because we only one run tool at a time

(forgot to commit this a while ago)

add xattr read support for getting the gtg project name

If the xattr module is available use it to check for 'user.gtg-project'
xattr before looking for the .gtg-project dotfile.

use setproctitle if possible

When gtgw is the parent of a long running process it is nicer to see
gtgw in the process list rather than a mysterious 'python' process.
If the setproctitle library (https://github.com/dvarrazzo/py-setproctitle)
is import-able, use it to set the process title to "gtgw".

pull out some logic to prepare for adding xattr support

optionally support specifying the project dir

add a gtgw "command" to help mark source trees with their go-names

show "fake" dir as an info message on stderr in order to not break pipelines

meet gtgw - the good to go wrapper