feat(shell/lean): add --index option

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
fix(library): remove LEAN_VERSION_FILE from Makefile.common, it breaks the build on Linux

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
fix(library/hott): remove hott_lib from build, it will be integrated in the standard library

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
feat(library/Makefile.common): generate .ilean files

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
chore(.gitignore): ignore .ilean files

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
chore(.gitignore): ignore .ilean files