Add options to enable/disable certain optimizations

[ghallak]

Fixes: #271

The following options are introduced:

• optimize_inliner
• optimize_inline_local_functions
• optimize_bind_subexpressions
• optimize_let_floating
• optimize_simplifier
• optimize_drop_unused_lets
• optimize_scode

By default, all options are implicitly set to true, and they should be disabled separately by explicitly setting them to false.

[radrow]

I don't like optimize_all. I would just set all of them to true by default - I would avoid inconsistent information