* Improve SMath wrapper error handling
1. Make CoolProp errors visible to SMath immediately, calling
get_global_param_string("errstring").
2. Use System.Exception with message instead of SMath own exceptions
where possible (to show the required message instead of irrelevant SMath
unconfigurable one); only retain SMath exceptions where it's necessary.
* Remove redundant text from release_readme.rst.txt; fixes#1105
