Rewrite the 'Types' chapter in coding standards.

Problem - current coding standards explicitly discourages
use of int, char, short etc, and recommends fixed types instead.

This is overly pedantic. The real problem, and the only problem we have
with types concerning portability, the inappropriate use of `long` is
too easy to overlook.

Thus,un-deprecate the types that are portable, for all practical purpose
i.e int, short, long long. Warning that char might be unsigned, though,
all compilers have appropriate flags.

Yet, use strongly wording to deprecate long and ulong, those are the types
that create real portability problems.

Author: vaintroub

CODING_STANDARDS.md

@@ -360,21 +360,20 @@ For example:
 my_function(thd, db_name);
 ```
 
-### Types
+### Integer types
 
-In general the usage of types such as `char`, `int` and `long` should be discouraged but there are shortened versions of the unsigned variants available for these in `my_global.h`.
-They can be different sizes across platforms and `char` can be either unsigned or signed depending on platform, and therefore are not portable.
-Instead these should be used as appropriate:
+The usage of types `long`  and `unsigned long` (and its `ulong` alias)
+in new code is *strongly* discouraged. Its use brings no advantages,
+only portability problems between Windows and Unixes.
 
-* 8-bit signed / unsigned int -> `int8` / `uint8`
-* 16-bit signed / unsigned int -> `int16` / `uint16`
-* 32-bit signed / unsigned int -> `int32` / `uint32`
-* 64-bit signed / unsigned int -> `int64` / `uint64`
-* Integer file descriptor -> `File`
-* Integer socket descriptor -> `my_socket`
+Instead of using `long`, use `size_t` and `ptrdiff_t` where appropriate,
+buffer sizes for example. For integer socket descriptor use `my_socket`.
 
-`size_t` and `ptrdiff_t` are used in the source where appropriate, buffer sizes for example.
-It should be noted that these are implementation dependent but are useful when used in the correct context.
+You may use types with fixed length, int32_t and similar, too. Yet, on all platforms we currently support,
+* `char` is 8 bit
+* `short` is 16 bit
+* `int` is 32bit
+* `long long` is 64bit
 
-Further types can be found in the `include/` directory files.
-There are also general utility functions in `mysys`.
+and the above is not likely to change for the decades to come. Those types are safe to use. When using `char`
+though, be aware that its signdness can depend on compiler flags, so do not assume it can take negative values.