update INSTALL

Don't tell users to clone recursively, because we want
to have some submodules that aren't always built, such
as libraries that are already present in the OS.
add submodules libatomic_ops and bdwgc
submodule maintenance

add libatomic_ops and bdwgc

provide version numbers for memtailor mathic mathicgb

include memtailor mathic mathicgb info in copyright string
Merge branch 'master' of github.com:Macaulay2/M2