Started a top-level meson.build file. This might actually work... maybe.

meson.build

@@ -0,0 +1,86 @@
+# 17 march 2019
+
+libui_OS = target_machine.system()
+libui_MSVC = meson.get_compiler('c').get_id() == 'msvc'
+
+libui_languages = ['c', 'c++']
+if libui_OS == 'darwin'
+	libui_languages += ['objc']
+endif
+
+libui_default_options = [
+	'default_library=shared',			# build shared libraries by default
+]
+libui_forced_options = {
+	'warning_level':	'3',			# always max warnings
+	'b_pch':			'false',		# we don't want precompiled headers
+	'b_staticpic':		'true',		# use PIC even for static libraries
+	'c_std':			'c99',		# strict C99
+	'cpp_std':			'c++11',		# strict C++11
+}
+foreach name, value : libui_forced_options
+	libui_default_options += [name + '=' + value]
+endforeach
+
+project('libui', libui_languages,
+	default_options: libui_default_options,
+	license: 'MIT')
+
+foreach name, value : libui_forced_options
+	actual = '@0@'.format(get_option(name))
+	if actual != value
+		error('sorry, but libui requires that option ' + name + ' has the default value ' + value)
+	endif
+endforeach
+
+libui_mode = get_option('default_library')
+if libui_mode == 'both'
+	error('sorry, but libui does not support building both shared and static libraries at the same time, because Windows resource file rules differ between the two')
+endif
+if libui_OS == 'windows' and libui_mode == 'shared' and not libui_MSVC
+	error('sorry, but libui currently does not support building a shared library with MinGW; use -Ddefault_library=static instead')
+endif
+
+libui_deps = []
+libui_libversion = ''
+libui_rpath = ''
+if libui_OS == 'windows'
+	# TODO c_winlibs and cpp_winlibs are the windows libraries
+elif libui_OS == 'darwin'
+	# TODO libraries
+	libui_libversion = 'A'
+	# the / is required by some older versions of OS X
+	libui_rpath = '@executable_path/'
+	# TODO min version 10.8
+else
+	gtk = dependency('gtk+-3.0',
+		version: '>=3.10.0',
+		required: true)
+	libui_deps += [gtk]
+	libui_libversion = '0'
+	libui_rpath = '$ORIGIN'
+endif
+
+libui_sources = []
+libui_extra_libs = []
+subdir('common')
+if libui_OS == 'windows'
+	subdir('windows')
+	install_headers('ui_windows.h')
+elif libui_OS == 'darwin'
+	subdir('darwin')
+	install_headers('ui_darwin.h')
+else
+	subdir('unix')
+	install_headers('ui_unix.h')
+endif
+libui_libui = library('ui', libui_sources,
+	dependencies: libui_deps,
+	build_rpath: libui_rpath,
+	install_rpath: libui_rpath,
+	install: true,
+	gnu_symbol_visibility: 'hidden')
+install_headers('ui.h')
+
+# TODO test
+# TODO examples