Simple pull merge or rebase

I added a couple of commands I regularly use.

0. pulls the current branch and the master branch and then merges the master into the current branch;
0. pulls the current branch and the master branch, then merges the master into the current branch and the current branch into the master branch;

I also made another couple of commands as rough equivalents for those who choose to rebase instead of mergeing (rebase-from-master and rebase-into-master).

All four commands check if there is anything to stash, stash it and pop the stash afterwards. They could be extended to merge/rebase from a custom branch (defaulting to master).