Add source map support. Fixes: #223, #250

[jamestalmage]

Fixes #223, #250

This adds basic source map support. Since transpilation of dependencies
is not merged yet, the sourceMapCache object and lookup is a little
premature (since we will only ever have one file that we can apply
apply source maps to).

[jamestalmage]

Because we use require-from-string, our source maps are never written to disk. This requires the implementation of the retrieveSourceMap callback. Final solutions for #189 and #177 will need to expand on this as well.

I do not know how expensive it is to load up source-map-support in each forked process like this.

Since all errors are serialized and transmitted over IPC before logging, It may be possible to defer the stack-trace transform until it has been transmitted back to the main thread.

[jamestalmage]

This needs #255 before it will pass on Windows. The Travis failure looks like a fluke.

Rebased onto master which contains referenced fix.

[sindresorhus]

Looks good 👍

[sindresorhus]

I do not know how expensive it is to load up source-map-support in each forked process like this.

Since all errors are serialized and transmitted over IPC before logging, It may be possible to defer the stack-trace transform until it has been transmitted back to the main thread.

Let's do some benchmarking before we start investigating this. Might not make a difference.