Don't crash on deprecated rules, but print a warning about them

[kivra-pauoli]

Bug Description

Elvis crashes with undef if e.g. a consumer is tweaking a default rule that's no longer present.

To Reproduce

Tweak macro_module_names and run Elvis.

Expected Behavior

Print a warning (a deprecation notice) for a given list of rules (we have them identified in the doc_rules), this way it'll be more pleasant to get results and the consumer can adapt to those.

rebar3 Logs

n/a

Additional Context

n/a

[kivra-pauoli]

Another way to do it would be to piggy back on the invalid_rule mechanism @bormilan introduced (with special notation for "deprecation") and an option to not exit on pre-warnings (or to exit on them if we want)

Rules:

• elvis_style, no_seqbind (deprecated before 1.0.0, so not worth adding)
• elvis_style, no_useless_seqbind (deprecated before 1.0.0, so not worth adding)
• ... all the other ones in doc_rules

[bormilan]

I like it!

[paulo-ferraz-oliveira]

Make sure that if a rule changed names we have a "legacy" file for it, at least until we decide to break major.

[paulo-ferraz-oliveira]

Another finding: makefiles was once a ruleset. Look at https://github.com/inaka/elvis_core/blob/1.0.0/src/elvis_rulesets.erl for more history (compare to what we have).