Add typedef for the result field

[lpatiny]

Currently the result is not really typed

The fields depends on the type of ID card and MRZ being analysed and it would be nice to have the type information in the result.

Linked to:

• interested dev #28

@mat2718 would you like to make a PR

[mat2718]

yupp!! im working through a small type issue but once im done with that ill make a PR

[mat2718]

#37

sorry this was so delayed in getting this in. let me know if you find any issues

[stropitek]

fields now has a definition for the record's keys.

Possible improvement is to narrow down the keys for each format with a discriminated union.