feat(library/unifier): add more information in error messages due to type errors when assigning metavariables

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
chore(util/lean_path): workaround 'spurious' warning produced by g++ in release mode

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
chore(util/list): add inline functions for commonly used patterns in list processing code

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
feat(library/hop_match): port higher-order (pattern) matcher to Lean 0.2, we still have to implement support for universe levels

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>