Feature request: explicit renaming list

[therontarigo]

It would be useful to have a command option for a list of things that should be renamed, in case they aren't. Since this would be useful primarily as a workaround for GLSL features that Shader_Minifier does not yet understand, the renamings should happen as for variables at global scope, with any instance of the identifier token being assumed a reference to this global item.

For example, from #237 :

buffer block_name{
  int member_name[];
};

shader_minifier --always-rename-list block_name,member_name would have these identifiers shortened. The required assumption that any instance of the identifier (as a C preprocessor would see it) is indeed a reference is to ensure that no further understanding by the tool of potentially unknown or unimplemented language features is needed.

[therontarigo]

Closing in favor of #378.