Integrate FlexBox layout

Integrate flexbox CSS property parsing.

Implement utils for computing flexbox-relevant sizes.

Adjust flexbox terminology

Parse FlexBox CSS properties, draft alignment code.

Draft flexbox layout

Fix release of CatTrap 0.4 (as I should've called it...)

Test table lowering

Support colspan on column elements.

Parse & apply CSS <table>-styling properties.

Allow styling table columns & rows!

Implement table layout.

Implement basic table layout.

Implement more of <table> layout

Improve concurrency, release 0.3, & (not in 0.3) better expose text info

Segfault/performance fixes.

Performance optimizations: Concurrency, & move download/styling/layout to out-of-thread.

Fix for Balkon update.

Fix inline sizing, handle length units for callers.

Integrate text-alignment support!