Document Thawing & Redeeming in Escrow.sol to Clarify Expectations of Indexer

[ColePBryan]

Enhance the inline documentation in Escrow.sol to clarify:

Thawing Process: Describe the role and implications of thawing funds from the escrow account before withdrawals.
Indexer Actions: Outline expected actions during a thaw that might reduce the escrow balance below the owed amount.
Transparency & Control: Highlight event emissions, account checks, and controls like redeem() and withdraw().
Potential Edge Cases: Touch on possible challenges or unusual behaviors indexers might encounter.
Let's ensure clarity and succinctness in our natdoc comments.

related #32