Live reloading should not exit after parse error

[paulsmith]

Currently if Pushup encounters any error, including a normal parse error while a developer is typing and saving, that causes the program to exit, this also causes the developer live reloading mode to exit as well.

We don't want the reloader to enter an infinite loop where it tries to re-run Pushup after an error condition but before any file change event has occurred. (Which was a previous bug noted in #4).

The desired behavior should be that, upon an error causing Pushup to exit, the reloader should stay running and upon detecting the next file change event, attempt to re-run Pushup.