Consider all amounts in multi-currency postings

[adamantike]

Describe the bug
For a transaction like:

2024/01/01 Cash transfer
    Assets:Savings
    Assets:Checking                          -20,000 INR
    Assets:Checking                             -500 USD

The posting returned by hledger will have a list of two amounts in the JSON key pamount, for the Assets:Savings account. Currently, we are only considering the first one we find, so the one for USD is ignored.

Related pull request: #149

Expected behavior
Correctly create postings for all currencies involved.

[ananthakumaran]

Sorry about the PR, I added a pull request template so that others will get more warning (I have it in the readme, but it's easy to overlook).

I will check this issue soon.