Linker error when using the libmuonpi library

[marvin5300]

Functions muonpi::http::content_type::json()and muonpi::http::content_type::html() are defined in the same header file as they are declared. This seems to lead to problems when using the library.

/usr/include/muonpi/http_response.h:72: multiple definition of `muonpi::http::content_type::html()'; CMakeFiles/rest_server.dir/rest_server/src/main.cpp.o:/usr/include/muonpi/http_response.h:72: first defined here
/usr/bin/ld: CMakeFiles/rest_server.dir/common_files/src/api.cpp.o: in function `muonpi::http::content_type::json()':