Started work on making atl build cross platform

[johnnyreilly]

Hey!

As discussed in #266 I wanted to help getting atl building cross platform. This PR starts that. Things to note:

• There was a typo in the build script; it should have read rm -rf dist but actually read rm -rf dict. I've corrected that and replaced rm -rf with rimraf as it's cross platform. Handily it was already a project dependency
• There was a typo in the name of a test; sourceamps should have been sourcemaps. Now it is
• I tested the build on Windows (my machine) and set up a build on AppVeyor which runs against TS 2.0 and TS@next. I added a build badge to the README next to the Travis build.
• Build-wise things were fine. However, there's one failing test (got this on my machine and you can see this in the AppVeyor build):

 10 passing (11s)
 2 pending
 1 failing

 1) main test should load tsx files and use tsconfig:

     AssertionError: expected 1 to equal 0
     + expected - actual

     -1
     +0

     at Context.<anonymous> (C:\source\awesome-typescript-loader\src\test\index.ts:59:49)
     at Generator.next (<anonymous>)
     at fulfilled (C:\source\awesome-typescript-loader\dist\test\index.js:4:58)

I haven't looked at the tests yet and so there may be an obvious reason why this test is failing. I'm out of time for now. Any thoughts?

Prob doesn't make sense to merge this PR until the failing test is resolved but I thought I'd share where I'd got so far.

[s-panferov]

@johnnyreill I've finally managed to rework my basic test suite. Thanks for the example, it helped me a lot.

[johnnyreilly]

No worries!