add Gmsh mesh file parser

In this commit added mesh file io for modmesh, it lets modmesh has
capabilty to read third-party mesh generator generated file and convert
the content to a data structure that allow modmesh can use it to do some
calculation.

Currently mesh io only support Gmsh format.

cpp/modmesh/CMakeLists.txt

@@ -37,6 +37,7 @@ add_subdirectory(onedim)
 add_subdirectory(python)
 add_subdirectory(spacetime)
 add_subdirectory(view)
+add_subdirectory(io)
 
 set(MODMESH_ROOT_HEADERS
     ${CMAKE_CURRENT_SOURCE_DIR}/modmesh.hpp
@@ -80,6 +81,7 @@ set(MODMESH_TERMINAL_FILES
     ${MODMESH_ONEDIM_FILES}
     ${MODMESH_SPACETIME_FILES}
     ${MODMESH_PYTHON_FILES}
+    ${MODMESH_IO_FILES}
     CACHE FILEPATH "" FORCE)
 
 set(MODMESH_GRAPHIC_FILES

cpp/modmesh/io/CMakeLists.txt

@@ -0,0 +1,23 @@
+
+cmake_minimum_required(VERSION 3.16)
+
+set(MODMESH_IO_HEADERS
+    ${CMAKE_CURRENT_SOURCE_DIR}/io.hpp
+    ${CMAKE_CURRENT_SOURCE_DIR}/gmsh.hpp
+    CACHE FILEPATH "" FORCE)
+
+set(MODMESH_IO_PYMODHEADERS
+    ${CMAKE_CURRENT_SOURCE_DIR}/pymod/io_pymod.hpp
+    CACHE FILEPATH "" FORCE)
+
+set(MODMESH_IO_PYMODSOURCES
+    ${CMAKE_CURRENT_SOURCE_DIR}/pymod/io_pymod.cpp
+    ${CMAKE_CURRENT_SOURCE_DIR}/pymod/wrap_Gmsh.cpp
+    CACHE FILEPATH "" FORCE)
+
+set(MODMESH_IO_FILES
+    ${MODMESH_IO_HEADERS}
+    ${MODMESH_IO_PYMODHEADERS}
+    ${MODMESH_IO_PYMODSOURCES}
+    CACHE FILEPATH "" FORCE)
+# vim: set ff=unix fenc=utf8 nobomb et sw=4 ts=4 sts=4: