Add flag to support for CQL

[gamorejon]

Add support for CQL which is used by Cassandra, ScyllaDB, YugeByte, etc. Works similarly to json in that it adds Marshal and Unmarshal methods.

[dmarkham]

@gamorejon were you not happy with this code?

[gamorejon]

There was a bug in the generated code that I fixed, but it's all working now and we are using in production. Mostly, I was unsure if you were open to taking it because adding the extra flag to main seemed to tip your code coverage tool over the threshold. I'll re-open if you are.

[dmarkham]

When I look though the code, it looked just fine I was more concerned about the introduction of a 3rd party include github.com/gocql/gocql currently I think everything we use is internal, my luck the next person will want to add some other cql library! Really wish the UnmarshalCQL did not require gocql.TypeInfo :cry: I guess if you have it all working and your happy with it, open it up maybe I can take some time try to get the coverage figured out.

[gamorejon]

Will do. Yeah, the dependency is not ideal -- especially since we don't care about supporting non-string CQL types -- but if it makes you feel better gocql is a low-level package for CQL which all the other ORM-like packages depend on. It's unlikely to be displaced for at least for a few years and TypeInfo is an interface so things still work with any forks. The ScyllaDB guys (they are a Go shop, for everything except the core DB) maintain a fork of gocql for gocqlx which we use and there are no issues.

[codecov-commenter]

Codecov Report

Merging #31 into master will increase coverage by 0.00%. The diff coverage is 57.14%.

@@           Coverage Diff           @@
##           master      #31   +/-   ##
=======================================
  Coverage   66.14%   66.15%           
=======================================
  Files           3        3           
  Lines         449      455    +6     
=======================================
+ Hits          297      301    +4     
- Misses        140      142    +2     
  Partials       12       12           

Impacted Files	Coverage Δ
stringer.go	61.11% <40.00%> (-0.12%)	:arrow_down:
enumer.go	100.00% <100.00%> (ø)
sql.go	100.00% <0.00%> (ø)

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