DOC: minor update to coding style file

It used to still refrence includes/{types,proto,common}/, now turned
to import/ and haproxy/.
diff --git a/doc/coding-style.txt b/doc/coding-style.txt
index 24550f1..d60a876 100644
--- a/doc/coding-style.txt
+++ b/doc/coding-style.txt
@@ -1,4 +1,4 @@
-2015/09/21 - HAProxy coding style - Willy Tarreau <w@1wt.eu>
+2020/07/07 - HAProxy coding style - Willy Tarreau <w@1wt.eu>
 ------------------------------------------------------------
 
 A number of contributors are often embarrassed with coding style issues, they
@@ -1149,11 +1149,10 @@
 ------------
 
 Includes are as much as possible listed in alphabetically ordered groups :
-  - the libc-standard includes (those without any path component)
   - the includes more or less system-specific (sys/*, netinet/*, ...)
-  - includes from the local "common" subdirectory
-  - includes from the local "types" subdirectory
-  - includes from the local "proto" subdirectory
+  - the libc-standard includes (those without any path component)
+  - includes from the local "import" subdirectory
+  - includes from the local "haproxy" subdirectory
 
 Each section is just visually delimited from the other ones using an empty
 line. The two first ones above may be merged into a single section depending on
@@ -1163,19 +1162,17 @@
 possible in alphabetical order so that when something is missing, it becomes
 obvious where to look for it and where to add it.
 
-All files should include <common/config.h> because this is where build options
+All files should include <haproxy/api.h> because this is where build options
 are prepared.
 
-Header files are split in two directories ("types" and "proto") depending on
-what they provide. Types, structures, enums and #defines must go into the
-"types" directory. Function prototypes and inlined functions must go into the
-"proto" directory. This split is because of inlined functions which
-cross-reference types from other files, which cause a chicken-and-egg problem
-if the functions and types are declared at the same place.
-
-All headers which do not depend on anything currently go to the "common"
-subdirectory, but are equally well placed into the "proto" directory. It is
-possible that one day the "common" directory will disappear.
+Haproxy header files are split in two, those exporting the types only (named
+with a trailing "-t") and those exporting variables, functions and inline
+functions. Types, structures, enums and #defines must go into the types files
+which are the only ones that may be included by othertype files. Function
+prototypes and inlined functions must go into the main files. This split is
+because of inlined functions which cross-reference types from other files,
+which cause a chicken-and-egg problem if the functions and types are declared
+at the same place.
 
 Include files must be protected against multiple inclusion using the common
 #ifndef/#define/#endif trick with a tag derived from the include file and its