git-branch-switch.sh added

Usage: git-branch-swtch <branch>

Makes branch <branch> the current branch, resets the index to
be identical to <branch>, but the working copy remains unchanged.

For now, only switching to local branches is supported, although
it should be possible to change to remote branches, tags or even
arbitary commits.

Signed-off-by: Eddy Petrișor <eddy.petrisor@gmail.com>
git-config.sh: my usual git aliases and preferences

Signed-off-by: Eddy Petrișor <eddy.petrisor@gmail.com>