send pre/post code context for exceptions and errors

[modethirteen]

Adds lines of code before and after the "code" line, as described in https://rollbar.com/docs/api/items_post/. We've been using this @MindTouch for a couple years with good results.

I didn't write a test as it uses file() to load source files into arrays. If you think a test is necessary I can create an abstraction for file() that is mockable.

[Crisfole]

Hey @modethirteen You're the man! This all looks really great.

If you don't mind writing a test we'd really appreciate it! I realize this involves refactoring the file reading a bit. Let me know if you need anything from us. We'd be happy to offer you any assistance you need.

[modethirteen]

@Crisfole no problem, i'll have the update shortly

[modethirteen]

@Crisfole updated and tests added

[Crisfole]

@modethirteen Nice! Thanks for that. I'll inspect later today, and get this merged in ASAP.

[modethirteen]

@Crisfole sounds great -- does a new tag get cut after that? it would be great it we were running the mainline releases.

[nocive]

@Crisfole any chance this will get merged soon?

[Crisfole]

@modethirteen @nocive I'd like to merge this soon. Tagging and releasing would need at least one extra set of eyes.

[Crisfole]

@brianr Take a peek? This looks good to me and it's tested.

[Crisfole]

Testing this locally right now and then I'll merge

[Crisfole]

Took a bunch longer because I discovered we didn't actually show the pre/post code yet, but had to make sure. This is fanstastic. Thank so much @modethirteen