Check if user-defined class names conflict with built-in data types

[zachcran]

Is this pull request associated with an issue(s)? No.

Description There is currently no checking for whether user-defined class names conflict with either built-in data types of CMakePPLang or other function signatures that may be defined in CMakePPLang or CMake. This PR solves part of the issue by checking user-defined class names against a list of built-in data type identifiers defined by CMakePPLang.

TODOs

• [x] Document usage of the cpp_check_conflicts() utility function in the user documentation if this work looks good.
• [x] Write individual tests for cpp_check_conflicts() if this work looks good.

[zachcran]

@ryanmrichard Please look over what I have so far and let me know what you think. I don't want to do the final user documentation write-up or very thorough unit testing until I know I am going in the right direction.

[zachcran]

@ryanmrichard Assuming these tests pass (which already pass on my local system), this is r2g