[Minor] Import lua-argparse library

CMakeLists.txt

@@ -1358,6 +1358,7 @@ ENDFOREACH(LUA_LIB)
 
 # Install lua fun library
 INSTALL(FILES "contrib/lua-fun/fun.lua" DESTINATION ${LUALIBDIR})
+INSTALL(FILES "contrib/lua-argparse/argparse.lua" DESTINATION ${LUALIBDIR})
 
 IF(ENABLE_TORCH MATCHES "ON")
 	INSTALL(FILES "contrib/moses/moses.lua" DESTINATION ${LUALIBDIR})

contrib/lua-argparse/LICENSE

@@ -0,0 +1,20 @@
+The MIT License (MIT)
+
+Copyright (c) 2013 - 2018 Peter Melnichenko
+
+Permission is hereby granted, free of charge, to any person obtaining a copy of
+this software and associated documentation files (the "Software"), to deal in
+the Software without restriction, including without limitation the rights to
+use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
+the Software, and to permit persons to whom the Software is furnished to do so,
+subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
+FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
+COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
+IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
+CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.