Detailed gains statement should contain NAV and Folio

[the-solipsist]

Currently the detailed gains statement does not contain the NAV at which the MF redemption took place, even though the NAV is available in the statement.

The following columns are available in the {basename}-gains-detailed.csv:
FY,Fund,ISIN,Type,Units,Purchase Date,Purchase Value,Stamp Duty,Acquisition Value,Sale Date,Sale Value,STT,LTCG Realized,LTCG Taxable,STCG

My request is to add NAV to that list.

Since adding it in the middle may break some scripts for users, perhaps it may be best to add it after STCG.

There's also a open request to add PAN to this list: #44

[the-solipsist]

It'd be nice to have the folio number as well in the detailed gains statement.

[the-solipsist]

One field which is a must-have is "transaction type" (called "type" in the transactions CSV), which should either be REDEMPTION or SWITCH_OUT. While I'm importing transactions into hledger, I treat these two separately.

EDIT: I just realized that the transaction type by itself is not reliable, and some SWITCH_OUT transactions are wrongly labelled REDEMPTION with a description that says Lateral Shift Out.

One other field which would be nice to have is "advisor".