Pyth integration

[ameliatastic]

Adding Pyth integration, partially because I wanted to see it happen and partially because it was easy enough that my commits here can be used as a tutorial for anyone that wants to add another Seahorse module (whether it's for an external program or otherwise).

The first 3 commits add a working (at least, it compiles lol) + minimal support for Pyth price feeds. I wrote everything at the same time but split the actual push into 3 separate commits for readability:

• The first commit does some background tasks that aren't needed each time a module is added
• The second commit does some setup for the eventual Pyth module (adding a new data file which is read in build.rs, worth a look if you need to add compile-time generated data)
• The third commit does the bulk of the work. Lots of files being modified but most of the changes are adding a couple of lines here or there to make the compiler aware of the new module/the new module's accounts.

Hope this helps!

Closes #46

[mcintyre94]

This is awesome! The only concern I'd have is how much of an impact it has on deploy cost for projects not using Pyth. I'm not really sure I have a good understanding of the implications of it being included by default.