lmake tries to find a makefile in the current working-directory or its
ancestors and invoke the makefile if found. If a makefile is not found,
it calls lean directly. This is also used for flycheck-lean.
Usage:
$ lmake
$ lmake all
$ lmake clean
$ lmake basic
$ lmake basic.lean
$ lmake /home/user/projects/lean/library/.../basic.lean
$ lmake --flyinfo --flycheck basic
