Fixes #937 - Adds HTTP method and URL to exceptions.

[dhermes]

@jgeewax Taking #938 over since it lingered.

@tseaver I rebased and will shortly send another commit addressing review feedback.

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[dhermes]

@tseaver PTAL

The things left unaddressed from the last PR were as follows:

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From @tseaver @jgeewax: Wasn't sure about a couple things, so wanted to ask...

1. Name of the variable (request_string). Seems expressive, but would rather pass a request object or something similar. Should I rename? Or pass two (method and url) on to make_exception?
2. Assembling the request string in the make_exception call (seemed like it might be better done on a separate line?)

From @dhermes: Should we have a newline somewhere in the error message if it gets too long? (I lean towards no because of line wrapping.)

[tseaver]

request_string seems wrong -- how about description or info?

I'm -0 on injecting a newline (thinking e.g. about logfiles: human readability vs. parsing by machine).

[dhermes]

WDYT of error_info or extra_error_info?

[tseaver]

error_info SGTM.

I've closed #938

[dhermes]

@tseaver Are we all good then?

[tseaver]

LGTM

[jgeewax]

LGTM - sorry for letting this linger. Thanks for cleaning it up for me :(

[dhermes]

No worries @jgeewax