MEDIUM: mux-h1/h1-htx: move HTX convertion of H1 messages in dedicated file

To avoid code duplication in the futur mux FCGI, functions parsing H1 messages
and converting them into HTX have been moved in the file h1_htx.c. Some
specific parts remain in the mux H1. But most of the parsing is now generic.
diff --git a/include/common/h1.h b/include/common/h1.h
index 0d652e7..5ed26fa 100644
--- a/include/common/h1.h
+++ b/include/common/h1.h
@@ -94,6 +94,8 @@
 #define H1_MF_NO_PHDR           0x00000400 // don't add pseudo-headers in the header list
 #define H1_MF_HDRS_ONLY         0x00000800 // parse headers only
 #define H1_MF_CLEAN_CONN_HDR    0x00001000 // skip close/keep-alive values of connection headers during parsing
+#define H1_MF_METH_CONNECT      0x00002000 // Set for a response to a CONNECT request
+#define H1_MF_METH_HEAD         0x00004000 // Set for a response to a HEAD request
 
 /* Note: for a connection to be persistent, we need this for the request :
  *   - one of CLEN or CHNK