VaultInk 0.58.0

A format filter for the Library, Search in Book that shows the words on the page, and battery drain per hour (kos25k #18, #24, #20).

• Library: a gear button in the header (left of search and refresh) picks which formats are listed: EPUB, PDF, TXT, Markdown, XTC, CBZ. Same list in Settings > Library, with a switch to hide the gear. PDFs are listed now; the list is rebuilt once after the update.
• Search in Book: the words are shaded on the page. A bar at the bottom steps to the previous or next hit; the arrow at the bottom right goes back to where you were, "Stay here" keeps the page. While looking at hits, your reading position, reading time and sync are left alone. Settings > Reader: show it in the More menu or not, and search the whole book or only up to where you are.
• Battery: drain per hour asleep and awake, after a few days of use. What each app draws can't be measured, so it says so.

Tested in the simulator and on the computer, not on a device yet. Full list: CHANGELOG.md.