docs: rework/update install.html

docs: rework/update install.html

Still far from perfect, but a few small steps in the right direction.

 - Split build systems, compilers, third party tools
 - Mention building mesa for Android (part of AOSP)
 - Drop explicit "other" dependencies. Reference to disto methods to
get them.
 - HTML 4.01 Traditional compliance fixes - mixed ul and br tags.
 - nuke dead links README.{CYGWIN,VMS}

v2: Squash typos, add note about buggy flex 2.6.2 (Eric), add Suse
zipper command (Tobias).

Signed-off-by: Emil Velikov <emil.velikov@collabora.com>
Reviewed-by: Brian Paul <brianp@vmware.com>