Add meson build

[whs]

This PR add Meson build for libthai

Notable changes:

• Configure options --enable-ansi is removed, as modern compilers should be quite mature now
• Configure options --enable-debug is replaced by --buildtype=debug
• This do not build each sub libraries then merge into one large library, instead all source is built all at once. I believe the old setup was done for incremental compiling, which Meson should already have done that.
• test-{thbrk,thwbrk}.sh are no longer used as it only wrap the actual test with env, which is a Meson feature. (test-thcoll.sh is still used)
• This contains wrapfile for https://github.com/tlwg/libdatrie/pull/22 which points to my last commit. If the build environment do not have datrie installed, Meson will download and build Datrie automatically.
• I've renamed all .cvsignore to .gitignore
• Seems that /Makefile.am do not contains SUBDIRS = man (intentional? bug?), so the man directory is not included in autotools archive building. In Meson archive building the man directory will be included.

[whs]

Windows test:

The code & data builds fine in mingw64. All tests passed except thcoll. thcoll requires diffutils and even with that installed thsort.exe doesn't output anything (it supposed to print usage if no args are provided).

As for meson-msvc (-D dict=false), tests also passing after applying a MSVC fix from !12