syncany formula

See https://github.com/syncany/syncany and https://www.syncany.org

Some fiddling with their install was required, but not much.

I don't really use this so I may not be the best source of information, I just wanted to mess around with it and creating a formula was preferable to using their install.

I'll reference this PR from the syncany repo and see if they have any comments.
Can this test be modified to do something more substantial than e.g. `--version` or `--help`? See `cmake.rb` for an example of an application formula with a good test and `tinyxml2.rb` for an example of a library formula with a good test. Thanks!