Applying interest rates to a Trove’s debt (borrower ops, batch, SP ops, sending funds to SP)

[RickGriff]

Applying interest rates to a Trove’s debt

Calculating pending interest

• Do debt * (1+interest_rate)**t where t is time passed in chosen time units since last update (blocks, minutes, etc), and interest_rate is the per-time-unit rate set by the borrower

Applying the interest

• Update the recorded debt and record the current block.timestamp as lastUpdateTimestamp
  A Trove debt getter function returns recorded debt, pending interest, and up-to-date interest (i.e. including pending interest)
• Mint the BOLD, and send it to the destination contract (e.g. the yield router?)

Interest is calculated and applied when:

• Borrower touches their Trove
• Permissionless batch function appyInterestToTroves is called with a list of Troves passed as a param
• SP deposits are touched. The SP functions take a single Trove address (/NFT ID), and calc and apply its interest

[bingen]

See #85 and #102