Meson port instead of using CMake as I ran into issues with the
src directory (where uchardet.h is located) not being appended
to the include path, and on Windows I ran into a Meson issue
where a -D macro definition was being interpreted as a filename.
In the end a Meson port seemed simpler than working out the CMake
issues, as the CMakeLists.txt files were straightforward and easy
to port.
Note that because of the directory structure of the uchardet source
I had to change the include directive from uchardet/uchardet.h
to just uchardet.h. This is actually more in line with the uchardet
pkg-config file, which appends /usr/include/uchardet to the include path.
uchardet will report that a file is "ascii" if the first page has no bytes
>127, so we need to actually look at the entire file in case the first higher
byte is later in the file.
