Applied some of clang-tidy fixes

Support for custom EOL per formatter -Thanks @emadwill 

Fix indentation in tests/catch.hpp:2916

Compiling with -Wmisleading-indentation triggers warning:
/data/Git/spdlog/tests/catch.hpp: In member function ‘bool Catch::TestSpec::Filter::matches(const Catch::TestCaseInfo&) const’:
/data/Git/spdlog/tests/catch.hpp:2913:17: warning: this ‘for’ clause does not guard... [-Wmisleading-indentation]
                 for( std::vector<Ptr<Pattern> >::const_iterator it = m_patterns.begin(), itEnd = m_patterns.end(); it != itEnd; ++it )
                 ^~~
/data/Git/spdlog/tests/catch.hpp:2916:21: note: ...this statement, but the latter is misleadingly indented as if it were guarded by the ‘for’
                     return true;
                     ^~~~~~

CMake explicit language

CMake 3.1 is used in main CMakeLists file, no reason not to use it in example.
Threads::Threads is introduced in cmake 3.1.

Marking project as CXX will disable detecting C compiler and other checks.
Removed 'INCLUDES DESTINATION' as it made the include path appear doubled.

Fix compilation error with GCC 8