feat(library): add definitions_cache datastructure for implementing .clean files

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
chore(shell/lean): rename shortname for --luahook option

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
feat(frontends/lean): add option --cache

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
refactor(library/tactic/expr_to_tactic): use annotations for implementing 'by'

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
feat(library/Makefile.common): use new --cache/-c option at Makefile.common

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