make: exclude README.md from html creation.

Uses the filter-out Make text function

"Returns all whitespace-separated words in text that do not match any of
the pattern words, removing the words that do match one or more."

http://www.gnu.org/software/make/manual/make.html#Text-Functions
make: exclude FAQ, DESIGN, LAYOUT
make: add filter dependencies to html recipe
Merge pull request #94 from aaren/fix-makefile-readme-html

Don't generate README.html (and others)