New tests!

@benstepp waded into the center of Gatsby and refactored one of the core functions AND setup a test framework AND added a number of tests. Awesome! #232

Bug fixes

• @BerkeleyTrue fixed route => template matching which was broken for some edge cases #230
• @BerkeleyTrue pointed out that errors in gatsby-node.js were being swallowed. @KyleAMathews fixed that in 859e412
• The Autoprefixer plugin was being added to the Postcss multiple times which @KyleAMathews fixed in dd2e960

Developer Experience (DX) improvements

• @michaeljdeeb added a check that hard-coded paths in pages have a path prefix. This is a problem that's bit several people as it's easy to miss #223. Invariants are awesome!
• @alehlopeh added a new cli command gatsby serve-build so you can easily check that your built site is working as expected. #237

Thanks everyone!