Update usage information for v0.3.2

[wymcg]

Update usage information in the README and on the website with the new options.

• Single-path plugin selection with --path changed to multi-path plugin selection with --plugin (Better plugin input scheme #58)
• --map-path was renamed to --mount, with minor usage changes (Change --map-path to mount #93)
• Several orientation and wiring options were added, including --vertical and the mirroring flags (Add vertically wired matrix support #86, Add ability to mirror matrix #87, Add ability to rotate matrix vertically #91)
• --gpio, --dma, and --frequency options were added (Add LED controller options #83)