Upcoming breaking changes

[lorenzwalthert]

These are probably candidates for release 2.0:

• remove save_after_styling env variable. Already deprecated.
• more_args must come last and have no default in create_style_guide().
• set base_indention and indent_by to integer default values from numeric.
• #796.
• style_pkg() should by default include all file types, plus also find these files everywhere in the package, e.g. R Markdown not just for README.md and in vignettes/.

Cache related

• cache_activate() and cache_clear() should have default to the option styler.cache_name, not NULL and then overwrite the option.
• cache_clear should probably not deactivate the cache.

Do this wisely with https://emptysqua.re/blog/api-evolution-the-right-way/.