Add support for cubic meters per second (CMS)

[lbutler]

I've added support for cubic meters per second, the tests are very basic and cover the most simple cases.

I haven't modified anything under src/outfile but can push another commit if we want to update and there is support for adding CMS flow units into EPANET.

Fixes #712

[LRossman]

I checked the changes and they look ok. If you want to want to update the src/outfile files then:

• insert ** 10 = cubic meters/sec at line 298 in epanet_output.c
• change line 36 in epanet_output_enums.h to ENR_CMD = 9,
• insert ENR_CMS = 10 at line 37 in epanet_output_enums.h