C language port of the library

[tenortim]

This is not an issue per se, but I couldn't think of another way to approach this.
I was looking for a "small" (i.e. not libopenssl) hashing library in C, but didn't find anything. This library is perfect, but is, obviously, in C++.
So, I have ported the code back to C with as few changes as I could. I have not yet ported the tests, but running digest against a set of random files yields the same checksums from both the original and C version which gives me some confidence that I didn't introduce any glaring bugs.
The code retains all copyright notices and statements that Stephan is the original author/owner.
I was considering posting this to github, and realize that the license allows for this but wanted to get your blessing before doing so. If you were interested in adding the repo to github.com/stbrumme, that would also be great.