Add string.c to CMakeList.txt
Add basic ws_value_string implementation
Add method stubs to string.c

Conflicts:
	src/values/string.c

Conflicts:
	src/values/string.c
Add implementation of ws_value_string_init()
Add implementation for ws_value_string_new()
Add implementation for ws_value_string_get_str()
Add implementation for ws_value_string_set_str()
Add implementation for value_string_deinit()
Merge pull request #168 from xVin/add-string_value_type

Add string value type