Setup

[PerezHz]

@MasonProtter, this is an awesome package, it's really nice that you're bringing scmutils to Julia! This is a small contribution, but I hope it helps!

This PR adds some essential setups which help with code development, namely:

• Update REQUIRE with minimum required versions for dependencies
• Add appveyor.yml, .travis.yml, and .codecov.yml

[PerezHz]

Update: added differentiation rules for sin, cos and added simple pendulum test

[MasonProtter]

Thanks Jorge! I appreciate the contribution!