Syntax hightlight of keywords after `=`

Nobody has claimed this yet.

In this issue description actual issues are described *below* related screenshots.


* `object` and `struct` should be like `class` or like `object`

There are also some minor things that look weird:
* Both `G`, `AstHelpers` and `Gmap` are modules but only first two are italic...

* Why labelled arguments are not italic but function itself and unlabelled arguments are?

* `module` keyword is not colored
* Color of modules (`PluginRes` and `Make`) are the same as constructor's (`Lident`) that could be misleading.
* `end` keyword may have the same issue that `object` and `struct` from the title of the issue. It seems that The Highlighter treat these keyword as syntactic garbage like parenthesis... Well, they are is some sense parenthesis ... but I'm not sure that it is a good idea.

* Some keywords have different colors. It seems that it is fine to have `open` and `inherit` of the same color because they do not defined new names... It may be a good idea to separate keywords that define different sorts of concepts but why the bottom let is blue (and not purple) then?

Review the screenshots and reported cases for `object`, `struct`, `module`, `end`, `let`, modules, constructors, and labelled arguments. The issue names no files or tests, so first locate the syntax-highlighting entry point for these Reason/OCaml constructs. Done means the affected keywords and identifiers use consistent, intentional colors and styles.

Written by the indexing model from the issue text.