Github Releases: Various small fixes:

1. Check for proper permisions before pushing.
2. Check that the file doesn't already exist before updating, preventing errors.

This should fix #126.
Merge pull request #128 from Joshua-Anderson/releases-patch-2

Github Releases: Various small fixes:
Bump version to 1.5.9.

The previous commit d0bcee7 was wrongly tagged, but
I am not retagging.
Fix version numbering when TEENY = 9
Define digits correctly