Public enum ToString/FromString and ToType/FromType

[emgre]

Closes #239.

All the public enums now expose a ToString and FromString, as well as a ToType and FromType for easy conversion from client side.

[emgre]

The enum utilities are now in [EnumName]Spec static class, with an enum_type_t typedef. So it is more easy to use in templates.

I also added a to_human_string for log values, and to_string for config-style strings.

[codecov]

Codecov Report

Merging #308 into develop will decrease coverage by 7.5%.
The diff coverage is 1.78%.

@@             Coverage Diff             @@
##           develop     #308      +/-   ##
===========================================
- Coverage    52.14%   44.63%   -7.51%     
===========================================
  Files          447      486      +39     
  Lines        18148    21202    +3054     
===========================================
+ Hits          9463     9464       +1     
- Misses        8685    11738    +3053

Impacted Files	Coverage Δ
cpp/lib/src/app/parsing/CountIndexParser.cpp	59.72% <ø> (ø)	⬆️
cpp/lib/src/app/APDULogging.cpp	100% <ø> (ø)	⬆️
cpp/lib/src/link/LinkFrame.cpp	94.93% <ø> (ø)	⬆️
cpp/lib/src/master/MasterContext.cpp	83.26% <ø> (ø)	⬆️
cpp/lib/src/app/parsing/RangeParser.cpp	80.48% <ø> (ø)	⬆️
cpp/lib/src/app/parsing/CountParser.cpp	82.92% <ø> (ø)	⬆️
cpp/lib/src/outstation/OutstationContext.cpp	92.17% <ø> (ø)	⬆️
cpp/lib/src/app/parsing/FreeFormatParser.cpp	35.29% <ø> (ø)	⬆️
cpp/lib/src/gen/UserOperationSerialization.h	0% <0%> (ø)	⬆️
cpp/lib/src/gen/TimeSyncMode.cpp	0% <0%> (ø)
... and 134 more

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