Alignment options

[siseval]

Added enums for vertical and horizontal alignment, and expanded the config loader to find fields v_alignment and h_alignment. I also added these to the README.

v_alignment=bottom does leave a slightly bigger gap at the bottom than v_alignment=top does on top, as render_height over-estimates the height of the full render.

Otherwise seems to work :)

[areofyl]

The feature makes sense but the code needs a few fixes before merging:

1. Style: 2-space indent, K&R braces (opening brace on same line), char * not char*. This is just to match the rest of the codebase
2. Add static to get_alignment_padding()
3. Add continue; after the config parsing blocks so they don't fall through
4. Move the get_term_size() call out of the per-frame loop. Compute alignment once and recompute on SIGWINCH

[siseval]

Think I've cleaned up all the inconsistent syntax. Added continues in both config parse blocks. Terminal size is now calculated once on startup, and in the if (term_resized) block you already had, and cached in term_rows and term_cols. get_alignment_padding() is also static now.