Move mg_ncasecmp and sister to common string utils

PUBLISHED_FROM=182c43c3bd82190cb816c8ebaddccc13a94950d0

docs/c-api/util.h/intro.md

@@ -8,7 +8,6 @@ items:
   - { name: mg_base64_decode.md }
   - { name: mg_base64_encode.md }
   - { name: mg_basic_auth_header.md }
-  - { name: mg_casecmp.md }
   - { name: mg_conn_addr_to_str.md }
   - { name: mg_fopen.md }
   - { name: mg_hexdump.md }
@@ -17,7 +16,6 @@ items:
   - { name: mg_match_prefix.md }
   - { name: mg_mbuf_append_base64.md }
   - { name: mg_mbuf_append_base64_putc.md }
-  - { name: mg_ncasecmp.md }
   - { name: mg_next_comma_list_entry.md }
   - { name: mg_open.md }
   - { name: mg_skip.md }

docs/c-api/util.h/mg_casecmp.md

@@ -1,10 +0,0 @@
----
-title: "mg_casecmp()"
-decl_name: "mg_casecmp"
-symbol_kind: "func"
-signature: |
-  int mg_casecmp(const char *s1, const char *s2);
----
-
-Cross-platform version of `strcasecmp()`. 
-

docs/c-api/util.h/mg_ncasecmp.md

@@ -1,10 +0,0 @@
----
-title: "mg_ncasecmp()"
-decl_name: "mg_ncasecmp"
-symbol_kind: "func"
-signature: |
-  int mg_ncasecmp(const char *s1, const char *s2, size_t len);
----
-
-Cross-platform version of `strncasecmp()`. 
-