Commit before branch, major refactor
Added testing, refactored file structure
Major Type Refactor: TransferFunction

Major refactor of TransferFunction type to make it more Julian.
- Added SISOTransferFunction type. This defines the base tf operations.
The user should never have to directly use this type.

- TransferFunction type now stores SISOTransferFunction objects in
a matrix parameter. All MIMO operations are now defined as matrix ops.

- Parametrized all types and relevant functions

- Types are now immutable

- Updated testing to reflect changes.
Assorted fixes for TransferFunction

-Fixed a few bugs in TF implementation
-Added conversion functions
-Added indexing, one(), zero()
-Fixed type consistency issues
Type Refactor of StateSpace

Refactored StateSpace code to be more Julian.
-Types are now parametric
-More efficient constructors and operators
-Fixed a few bugs in operator implementations
-Added test file for StateSpace
Attempt at Travis-CI Testing

Not sure if this will work, only way to know for sure is to test
it. Added .travis.yml file, and runtests.jl.
Added REQUIRE file, updated travis.yml