[gccsdk] SimpleGit

Hi,

Attached is a first-pass autobuilder recipe for SimpleGit
(https://github.com/sba1/simplegit). The resulting binary seems to work
well enough to clone repositories via https - I haven't tested it much
beyond that.

Issues are likely to be:

* Filename translation might need tweaking to allow easy control over the
rules that are used for each repository
* Likewise filetype translation is likely to need tweaking (e.g. support
for ,xxx suffixes in the repository).
* It's a bit slow - although a lot of that is likely to be due to
deficiencies in RISC OS.
* It's had minimal testing
* The recipe is a bit rough around the edges

I'll try and find the time to work on it a bit more over the next few
days/weeks, but figured it was a good idea to share it now while it's
still in this early state just in case someone else is eager to have a
play around.

This recipe builds libgit2 from the submodule that's imported by
SimpleGit. But I also have patches for building libgit2 from the
upstream libgit2 git repo, so I might experiment with them to produce a
libgit2 recipe which SimpleGit can then use instead.

Cheers,

- Jeffrey