Search field that sends to hoogle

A list of diagrams packages gets appended to the query.

issue #23

List of appended packages can be modified by changing variable
`PACKAGES` in `web/js/hoogle-search.js`. At the moment it is"

	var PACKAGES = '+diagrams-contrib +diagrams-lib +diagrams-core +diagrams-canvas \
	+diagrams-cairo +diagrams-rasterific +diagrams-svg +diagrams-builder \
	+diagrams-postscript +active +palette +diagrams-constraints'
Merge branch 'hoogle_search' of https://github.com/zudov/diagrams-doc into hoogle_search