Handle plus and minus identifiers better

[jupp0r]

This change improves handling of db identifiers:

• it handles "+" in identifiers
• it improves handling of identifiers that end with plus or minus like "Entity+" and "Entity-" as enum values that would otherwise produce conflicting values

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (e03773a) 90.35% compared to head (5049a50) 90.36%.

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Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #311 +/- ## ========================================== + Coverage 90.35% 90.36% +0.01% ========================================== Files 124 124 Lines 7162 7173 +11 ========================================== + Hits 6471 6482 +11 Misses 530 530 Partials 161 161 ```

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[go-jet]

I've changed my mind on this one. There were couple of bugs opened before for similar invalid character issues. To prevent any additional bugs opened, I've made a change that replaces all invalid ascii characters with they description.
In your case, you would still need to customize generator because minus and hyphen are the same character, and hyphen is first replaced with underscore, and underscores at the end of identifier are removed.