chore(*): add license badge

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
fix(library/Makefile.common): avoid error message when .d files do not exist

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
fix(library/Makefile.common): make OSX-compatible
chore(tests/lean): add 'expensive' file

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
fix(frontends/lean/elaborator): bug when mixing string and non-strict implict arguments

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
fix(frontends/lean/elaborator): remove duplicate entries in flyinfo data

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
fix(kernel/formatter): fixes #21

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
fix(frontends/lean): add hack for flycheck

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
feat(library/standard): add markdown documentation
feat(library/standard/logic/axioms): add import default
feat(library/standard/data/nat): port most recent nat to lean 0.2