zipapp: add compression (method), compresslevel options from Zipfile

Zipapp is meant to produce things that will be delivered to an end-user. In this way it should behave like most packaging tools and offer more "thorough" compression options, limited only by the version of the Python interpreter on the user's side (more specifically, their zipfile modules). As a result I believe we should be allowed to choose the compression method and compression level. Some seconds spent on the developer's computer can be minutes saved on downloading from a poor Internet connection.

My proposed API surface include two keyword-only parameters, compression and compresslevel, both having the same meaning and type as their Zipfile counterparts. The compression option should take precedence over the current boolean "compressed" option if it is not set to None; otherwise the settings, including the defaults for "compressed" apply.