fix: Let column names not invalidate Go field names

[rollulus]

Column names are less restricted than Go struct field names, which should be proper Go identifiers. Hence, column names cannot be translated directly into field names. This commit tries to address this.

Characters in column names that do not qualify as a Go identifier are stripped. The title casing as applied to underscores is applied to stripped characters.

[rollulus]

I wasn't sure about the e2e test naming convention. Also: thanks for this project!