Fix for issue 17: rename `concept` to `concepts` to fix clash with C++20 keyword

[willowell]

#17

[elmajime]

Hi, is there any plans to merge this branch ?

[willowell]

@elmajime Hi there,

Please note that oktal gave this an open source license, so you (or I!) can fork this repository and apply the fix.

My fix is obviously trivial enough that you can do it yourself :-)

This also does not preclude giving back via a PR across forks.

[LuisFilipeDias]

@oktal this is becoming more of an issue. https://releases.llvm.org/13.0.0/tools/clang/docs/ReleaseNotes.html#c-20-feature-support is also problematic, as it provides: C++20 Feature Support¶.

Can we go ahead and merge this into mainline? Thanks in advance.