rename: replace "compton" in the codebase

leftovers:

1) config file path. Has to implement compatibility functionalities before
  we can change it.

2) links in man pages. Has to migrate the repo first.

3) _COMPTON_SHADOW, it has become a defacto standard, so we have to keep
   supporting it.

4) dbus names, undecided whether we should/could change it.

Signed-off-by: Yuxuan Shui <yshuiv7@gmail.com>

meson.build

@@ -1,4 +1,4 @@
-project('compton', 'c', version: '7',
+project('picom', 'c', version: '7',
         default_options: ['c_std=c11'])
 
 cc = meson.get_compiler('c')
@@ -43,7 +43,7 @@ if get_option('modularize')
 	add_global_arguments(['-fmodules',
 	                      '-fmodule-map-file='+
 	                      meson.current_source_dir()+
-	                      '/src/compton.modulemap'],
+	                      '/src/picom.modulemap'],
 	                     language: 'c')
 endif
 
@@ -69,9 +69,12 @@ test_h_dep = subproject('test.h').get_variable('test_h_dep')
 subdir('src')
 subdir('man')
 
-install_data('bin/compton-trans', install_dir: get_option('bindir'))
+install_data('bin/picom-trans', install_dir: get_option('bindir'))
 install_data('compton.desktop', install_dir: 'share/applications')
+install_data('picom.desktop', install_dir: 'share/applications')
 install_data('media/icons/48x48/compton.png',
              install_dir: 'share/icons/hicolor/48x48/apps')
 install_data('media/compton.svg',
              install_dir: 'share/icons/hicolor/scalable/apps')
+
+meson.add_install_script('meson/install.sh')