chore(.travis.yml): set up travis-ci for backup and diff notification
feat(list.lean): proved reverse reverse theorem
Merge branch 'master' of github.com:leanprover/libraries
chore(Makefile): add Makefile

Add simple 'Makefile' to compile '.lean' files into '.olean'
files. It assumes that 'lean' is in the 'PATH' variable. If this is
not the case, you can run 'make' while specifying the pathname for
'lean' as follows:

    $ make LEAN=~/work/lean0.1/build/shell/lean
chore(.travis.yml): compile .lean to .olean and upload to dropbox
feat(nat/kernel)
Added le lt and a bunch of theorems
Some theorems still need a proof and are currently and axiom. nat_ind currently only compiles with the standard kernel, not the kernel in this folder