fix: add missing 'inline' in public headers

Author: lichray

include/httpverbs/c_file.h

@@ -34,6 +34,7 @@ namespace httpverbs
 namespace keywords
 {
 
+inline
 auto from_c_file(FILE* stream)
 	-> decltype(std::bind(
 	    fread,
@@ -46,6 +47,7 @@ auto from_c_file(FILE* stream)
 	    std::placeholders::_2, stream);
 }
 
+inline
 auto to_c_file(FILE* stream)
 	-> decltype(std::bind(
 	    fwrite,

include/httpverbs/stream.h

@@ -63,12 +63,14 @@ struct _request_sputn_cb
 namespace keywords
 {
 
+inline
 auto from_stream(std::istream& is)
 	-> _request_sgetn_cb
 {
 	return _request_sgetn_cb(is.rdbuf());
 }
 
+inline
 auto to_stream(std::ostream& os)
 	-> _request_sputn_cb
 {