Write documentation

[davvil]

We are adding every time more features (cool!), but we do not really document them (uncool). We should. Do we want to use github's wiki for it? We should also write a man page, in spite of its ugly syntax.

(Probably incomplete) List of things to document:

• [ ] FTS installation
• [x] Full list of options with explanation of options
• [x] FTS syntax, including the columns that can be searched in bibsearch
• [x] Config file options
• [x] 'custom_key_format' format
• [ ] FAQ with at least "I installed sqlite3 with FTS but it is still complaining" and "my searches that include '-' or ':' fail miserably"
• [ ] Call for help for .bib files

[mjpost]

A man page might be good. I like the approach of writing an extensive README and converting that to a man page somehow, or having bibsearch help pull it in somehow. I'll take a stab at this.