Use local jshint installation.

Fixes build errors when jshint is not installed globally.
Make it easier to use global binaries.

You can now set BIN_PREFIX if you'd rather use a global install of
node.js. You can also specify JSHINT_BIN, RECESS_BIN and UGLIFYJS_BIN
to use global or local installs as you like
Ignore errors if running make clean on clean repo

Mostly a cosmetic change, although it should now be work as expected to
run for example "make clean bootstrap" on a clean install.
Corrected .PHONY targets list
Removed docs dependency from gh-pages target

That target does not exist, so having it as a dependency does nothing.
Silence call to echo