Support author

[stepelu]

Disclaimer: I can barely code in go and had no prior feed expertise.
This PR adds support for the author information, all 4 feed types are supported with (limited) testing.

More details:

• author info is displayed below the date on the right pane when present
• author info is searchable
• HTML is stripped from author info
• for RSS I allow both dc:creator and (non-conformant) author as the latter is still somewhat used in practice, dc:creator has priority

The search fts4 table has been modified accordingly, but clearly this is not done properly following the "migration" approach, so changes there are needed.
I am also unsure about the formatting / spacing in the structs I modified, please feel free to re-arrange.
I am aware of #57, I noticed the presence of the author column in the items table and went ahead with this modifications on my side as I needed them for my use case.
Please feel free to reject if this development is not desired.

[nkanaev]

hi @stepelu. thanks for your efforts.

the author field was not included on purpose, as it:

1. provided little to no value for personal feeds, as they contained only a single author
2. required supporting multiple authors with corresponding metadata (name/url/avatar).

i do believe that having author information might be valuable for collective feeds, news feeds etc. but it's a little sacrifice i made. the main goal was to focus on the content itself & simplicity, rather than metadata information.

[stepelu]

provided little to no value for personal feeds, as they contained only a single author

Usually it is the case.
My main use case for RSS is to follow up arXiv articles, like in:
http://arxiv.org/rss/cs.LG
There, being knowing who are the authors is key information (to determine whether to check an article further or not).

required supporting multiple authors with corresponding metadata (name/url/avatar).

I am not sure this is so important, especially as conveyed info depends on the feed type.

Either way it is fine. Maybe I'll make my customized version public at some point in the future in case it is useful for someone else.