PDF Documentation needs updating

[willGraham01]

Having been working on #320, it is quite clear that the PDF documentation needs an update.

• There are some input variables like exdetintegral that are required but are not documented.
• The compact source condition/criterion is mentioned in the testing section of doc/developers but we don't actually have an explanation of what it is/means in the documentation.
• The input flags use_pstd and use_bli are not mentioned at all.
• The choice of interpolation scheme is not mentioned. Nor is it mentioned when one may wish to use cubic over band-limited or vice-versa.