Remove an unhelpful let binding
Add some missing docstrings
Give clearer names to helper functions

Previously, the names were minor variants of the corresponding
interactive function names. Rename to make it clear which functions are
internal helper functions.
Mark bog-prepare-bib-file as an internal function
bog-find-citekey-bib: Expand docstring
bog-find-citekey-bib-func: Reword docstring
bog-selection-method: Complete docstring
bog-citekey-from-heading: Correct docstring
bog-citekey-file-name-separators: Reword docstring
bog-citekey-as-search-url: Add argument to dosctring
Ignore bog-autoloads.el
Generate docstring for citekey selection functions