Travis now enabled

Group,

I went ahead an enabled travis-ci on the web-audio-api repo. It ensure that
the spec is neatly indented and has valid markup using the tidy program.

You can replicate the testing environment that runs on the test machines by
running (on an UNIX machine that has git and cmake):

$ make install_tidy
$ make check

and if this fails, you can do

$ make tidy

to call tidy with the appropriate options. Reading the tidy config file,
you can see what the rules are (it's pretty self explanatory and standard).

I've added a badge to the readme that tells us whether the current spec is
clean or not. More over, when opening a pull request, a nice bot will come
and tell you whether it's tidy-clean or not, and then you can push a
followup as needed.

It might spam us with emails, we'll see (I'm actually not sure if I'm the
one receiving them or what).

Cheers, and have a good weekend,
Paul.