renamed executable for integration with git

Git looks for commands in the form git-* when parsing command arguments.
Therefore, with this rename, we can call the program naturally:

git pull-request list
renamed executable to git-pr

find -type f | xargs sed -i 's/git pull-request/git pr/g'
find -type f | xargs sed -i 's/git-pull-request/git-pr/g'

See for discussion:
https://github.com/robinsmidsrod/App-GitHubPullRequest/pull/5
Change name of prq-token to pr-token

Was messed up after the previous rename. No need for git- prefix, we're
already in git. :)
Fixed some wide character in print errors on output

UTF8 output is now used, regardless of what your terminal is set to.