Cast inputs in the MATGAS parser to the correct type

[tasseff]

For example, I was running into an issue where base_pressure was being parsed as an integer. Wrapping the parsing with casts like

case["base_pressure"] = Float64(matlab_data["mgc.base_pressure"])

should correct this.

[ccoffrin]

I would expect this to be addressed by the generic Matlab parser. Maybe that parser needs a new feature to support specifying types for constant values?