[modernize] Use proper Enums and remove get_all

[jmarrec]

https://github.com/NREL/EnergyPlusRegressionTool/blob/212d62afb573d77c748f29817e4cf89858fd110d/epregressions/structures.py#L17-L33

Transition to use Enums, which makes get_all unecessary

from enum import Enum
class ReportingFreq(Enum):
    DETAILED = "Detailed"
    TIME_STEP = "Timestep"
    HOURLY = "Hourly"
    DAILY = "Daily"
    MONTHLY = "Monthly"
    RUN_PERIOD = "RunPeriod"
    ENVIRONMENT = "Environment"
    ANNUAL = "Annual"
    
In [2]: [x for x in ReportingFreq]
Out [2]: 
[<ReportingFreq.DETAILED: 'Detailed'>,
 <ReportingFreq.TIME_STEP: 'Timestep'>,
 <ReportingFreq.HOURLY: 'Hourly'>,
 <ReportingFreq.DAILY: 'Daily'>,
 <ReportingFreq.MONTHLY: 'Monthly'>,
 <ReportingFreq.RUN_PERIOD: 'RunPeriod'>,
 <ReportingFreq.ENVIRONMENT: 'Environment'>,
 <ReportingFreq.ANNUAL: 'Annual'>]

(each enum has a .name and a .value attribute too)

[Myoldmopar]

👍