as suggested in #1441.

generally U32 and unsigned are the same thing,
except when they are not ...

case : 32-bit compilation for MIPS (uint32_t == unsigned long)

A vast majority of transformation consists in transforming U32 into unsigned.
In rare cases, it's the other way around (typically for internal code, such as seeds).

Among a few issues this patches solves :
- some parameters were declared with type `unsigned` in *.h,
  but with type `U32` in their implementation *.c .
- some parameters have type unsigned*,
  but the caller user a pointer to U32 instead.

These fixes are useful.

However, the bulk of changes is about %u formating,
which requires unsigned type,
but generally receives U32 values instead,
often just for brevity (U32 is shorter than unsigned).
These changes are generally minor, or even annoying.

As a consequence, the amount of code changed is larger than I would expect for such a patch.

Testing is also a pain :
it requires manually modifying `mem.h`,
in order to lie about `U32`
and force it to be an `unsigned long` typically.
On a 64-bit system, this will break the equivalence unsigned == U32.
Unfortunately, it will also break a few static_assert(), controlling structure sizes.
So it also requires modifying `debug.h` to make `static_assert()` a noop.
And then reverting these changes.

So it's inconvenient, and as a consequence,
this property is currently not checked during CI tests.
Therefore, these problems can emerge again in the future.

I wonder if it is worth ensuring proper distinction of U32 != unsigned in CI tests.
It's another restriction for coding, adding more frustration during merge tests,
since most platforms don't need this distinction (hence contributor will not see it),
and while this can matter in theory, the number of platforms impacted seems minimal.

Thoughts ?

from 64-bit to 32-bit

for naming consistency

We link new manpages with gz compressed format of the target manpage.
I have not tested it on Windows. So just place a warning here.

The run_command is run from an unspecified directory. Therefore we cannot assume
which directory it is running our command.

Use files function instead of constructing path with meson.current_source_dir()

NOTE: This commit only tested on Linux (Ubuntu 18.04). Windows
build may not work as expected.

* Use meson >= 0.47.0 cause we use install_man function
* Add three helper Python script:
  * CopyFile.py: To copy file
  * CreateSymlink.py: To make symlink (both Windows and Unix)
  * GetZstdLibraryVersion.py: Parse lib/zstd.h to get zstd version
  These help emulating equivalent functions in CMake and Makefile.
* Use subdir from meson to split meson.build
  * Add contrib build
  * Fix other build
* Add new build options
  * build_programs: Enable programs build
  * build_contrib: Enable contrib build
  * build_tests: Enable tests build
  * use_static_runtime: Link to static run-time libraries on MSVC
  * zlib_support: Enable zlib support
  * lzma_support: Enable lzma support

and replaced by traditional macro constants.

Unfortunately, C doesn't consider `static const` to mean "constant"

to use structure for function parameters
as it expresses much clearer than a long list of parameters,
since each parameter can now be named.

it shall be possible to use benchfn
without any dependency on zstd.

by triggering the prefetching decoder path
(which used to be dedicated to long-range offsets only).

Figures on my laptop :
no content prefetch : ~300 MB/s (for reference)
full content prefetch : ~325 MB/s (before this patch)
new prefetch path : ~375 MB/s (after this patch)

The benchmark speed is already significant,
but another side-effect is that this version
prefetch less data into memory,
since it only prefetches what's needed, instead of the full dictionary.

This is supposed to help highly active environments
such as active databases,
that can't be properly measured in benchmark environment (too clean).

Also :
fixed the largeNbDict test program
which was working improperly when setting nbBlocks > nbFiles.

some details changed with introduction of gcc7

Remove unsigned to size_t promotion to fix implicit down conversion errors in clangbuild target.

will automatically truncate or repeat input as needed,
to create the requested nb of blocks.
default: nb of files, eventually increased appropriately if blockSize is set