This commit standardizes the various todos around the code a bit in a manner recognized by LDoc.
Besides drawing more attention by being displayed in the developer docs, they're also extractable with LDoc on the command line:
```sh
ldoc --tags todo,fixme *.lua
```
However, whether that particular usage offers any advantage over other search tools is questionable at best.
* and some random beautification
ReaderLink: make all links be a table (they were a table for PDF,
but a string for CRE) for clearer code. Also have location_stack
store them as tables, with additional properties.
Get original position of link source (and verify it is valid)
so we can show a marker there.
Also:
Hold on "Go back to previous location" to clear location stack.
Resists "Swipe to go back" when previous locations stack has just
become empty, and show a notification.
Fix wrong links with Swipe to follow nearest link on PDF documents.
Fix various inconsitencies: some occurences not highlighted
on displayed page; different occurences highlighted on same
page wheter we went there searching backward or forward; pages
with occurences simply just skipped when searching in one
direction, and not in the other...
To avoid edge cases, crengine will now give back results on up
to 3 pages, that we need to filter.
Bump base and crengine
Makes it easier to comply with UX style.
* Change "OK" to "Search dictionary" in Dictionary lookup to comply with UX style
* Change "OK" to "Search all text" in Fulltext search to comply with UX style
Tacked on but highly related:
* change "OK" to "Search Wikipedia" in Wikipedia lookup to comply with UX style
* change "OK" to "Set default" in ConfigDialog to comply with UX style
Chore:
* fixed up order of requires
