Add basic Travis CI configuration

I added a basic Travis CI configuration to make the build status more
transparent. I added a small logo to the bottom of the README with the
status and a link to the build.

@evancz after merging this you'd have to go to https://travis-ci.org
and enable the build for this project, just takes a couple of clicks.
See http://about.travis-ci.org/docs/user/getting-started/.

I tested this on my own github account and the configuration worked
(ie, it showed the same build errors on Travis that I'm experiencing
locally).
new instance for SS.Type
added some guards. todo turn this into correct Gen. still one failcase
Merge remote-tracking branch 'evan/dev' into arbitary-tipe
better gen and shrink, but stack overflows
turned off Data and Record types, found a bad test case with lambda
also should be able to check both sub-types are valid
really didn't need this
better shrinking and not-infinite-dump generation results in passed tests!
Merge remote-tracking branch 'evan/dev' into arbitary-tipe
used a more specific PP rendering to revert the changes to SS.Type pretty
Merge pull request #452 from johnpmayer/arbitary-tipe

Added pretty.parse tests for SourceSyntax.Type
restrict incoming ports to disallow data structures that contain signals, only "top-level" signals are allowed
Simplify the JS API for sending values to signal ports, making error handling more reasonable
Add the always function

I want it, I do not want to rename constant, and I think it is a good
name.
resolve conflict in README!
Merge branch 'jsl-add_travis' into dev
Get rid of the word "simply". It is a condescending word.
Move build status higher up
Add a test for port parsing and types

Partly addressing #442