CMake: Canonicalize rapidjson include path in RapidJSONConfig.cmake.

[bastianbeischer]

Having the path without relative components allows other projects to add the
RadidJSON_INCLUDE_DIRS as a system include directory, without causing problems
in the build.

[tencent-adm]

All committers have signed the CLA.

[bastianbeischer]

See discussion in:

MaskRay/ccls#383

(specifically the last comment)

[coveralls]

Coverage increased (+0.001%) to 99.922% when pulling c9b57bd on bastianbeischer:cmake into 01950eb on Tencent:master.

[coveralls]

Coverage increased (+0.001%) to 99.922% when pulling c9b57bd on bastianbeischer:cmake into 01950eb on Tencent:master.

[smancill]

I fixed issues with the install locations in PR #1454, see commits deecf8c and 425c1e7.

Would that fix the problem? I think using configure_package_config_file is better.

[bastianbeischer]

I fixed issues with the install locations in PR #1454, see commits deecf8c and 425c1e7.

Would that fix the problem? I think using configure_package_config_file is better.

Yes, your PR also fixes the problem.