consider ASSET_DIVIDEND transactions when computing return

[d-k-c]

When computing the returns of an asset, transactions of type ASSET_DIVIDEND are not considered. That makes the return rate computed by beangrow substantially different to rates reported by fund managers.

I could not find any justification as to why these transactions are ignored when computing the return rates, and this seems to confuse me as well as other users. See #23 and #26

At least with this small patch, users get a chance to try and see if they get the result they expected.

[blais]

Hmm, you mean to deal with a change in asset due to a dividend in shares?
How would you know that this change in ASSET (the posting) is the result of a dividend and not a purchase or sale?

[d-k-c]

Hmm, you mean to deal with a change in asset due to a dividend in shares?

Yes.

This is one of the example of #26.

2023-09-26 * "REINVEST - DIV - DIVIDEND REINVESTMENT"
  Assets:US:Vanguard:Roth:VTI                  0.817 VTI {212.9008 USD}
  Income:US:Vanguard:Roth:Dividends:VTI      -173.94 USD

This transaction is currently ignored when computing portfolio performance as the dividend is used to buy some shares, instead of being deposited on a cash account. So depending if I set up a Dividend Reinvestment Plan (DRIP) or not, the computed return is not the same.

How would you know that this change in ASSET (the posting) is the result of a dividend and not a purchase or sale?

Now, this is where I might be completely wrong, but I assumed a regular purchase or sale would have one posting being categorized as ASSET and another posting as CASH. The patch I propose here only applies if one posting in the entry is categorized as ASSET and another as DIVIDEND, so I'm relying on beangrow categorization to identify the transaction as a dividend reinvestment instead of a purchase/sale.