refactor!: mesgdef update, fix & other improvements

[muktihari]

1. Mesgdef

• Messages now receiving pointer to mesg, if mesg nil, it will return a struct with all fields will be set to its corresponding invalid value. Example: mesgdef.NewRecord(nil)
• Messages now use time.Time instead of typedef.DateTime or typedef.LocalDateTime, in real world use case this is more practical to work with native golang type time.Time.
• Messages now have methods for assigning values as syntax sugar:

mesgdef.NewRecord(nil).
	SetTimestamp(time.Now()).
	SetSpeed(1010).
	SetCadence(100).
	SetHeartRate(110)

2. Factory

• Now user can register message in the range that have not been taken by predefined message, this is useful since there are some messages that not specified in the Profile.xlsx but being used for internal use by some manufacturer.

3. Others

• Fix on decoder when trying to decode developer field but no field_description is declared was not consume the bytes occupied by that field that might causing decode error (only happen when we try to decode bad encoded fit file).
• Fit to Csv converter in converting developer fields is corrected.
• Typedefs that support registering manufacturer specific types is updated as well, similiar to the changes applied to factory