Add v0 technical spec

spec/overview.md

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+# Porter Protocol Technical Specification 
+
+It may help if we start with the simplest design - no factories - no convertibility - no upgradability -imagine we want to create just a single auction. 
+
+
+# EasyAuction
+@namaskar fill this out:
+
+We should probably follow how easyAuction is implemented with a single auction contract that holds all of the auctions. 
+
+
+
+
+# BondToken
+Upon the completion of a successful auction a new bond contract is deployed. Terms of the bond were determined by the auction. Bond tokens need minted and sent to investors who won the auction. 
+
+Bond token is an ERC20 token. 
+
+### Methods
+`mint()` `isAuction` // callable by the auction contract to mint bond tokens and send them to investors who won the auction
+
+`redeem()`  checks maturity date & bond standing - if it's past maturity date and the loan as been repayed then burn the bonds and send the repayment tokens to the address calling redeem() - maybe we follow the rocketpool method and calculate the % of total bond tokens a user holds, then allow them to claim that % amount of the total repayment tokens
+
+### State Variables
+`standing` // good | defaulted | paid 
+`maturityDate` // https://github.com/porter-finance/v1-core/issues/2
+
+# Flash Loans
+DAOs can use a flash loan to liquidate part of their collateral to pay back their debt. 
+
+## Examples
+Here are two exampls of how that would work. Fees are ignored for simplicity. 
+
+### Example 1:  
+A DAO owes 100m DAI to the porter protocol. They have 10,000 stETH (at $2000/eth, 20m USD) as collateral in the porter protocol. They also have 90m liquid DAI in their treasury. 
+1. DAO uses [Aave Flash Loan](https://docs.aave.com/developers/guides/flash-loans) to borrow 10m DAI
+2. DAO pays back their full 100m DAI porter debt (which releases their collateral)
+3. DAO withdraws their collateral and swaps some amount of it for 10m DAI on a DEX
+4. DAO repays Aave 10m DAI flash loan
+5. DAO now has their porter debt repaid and has their remaining collateral 
+
+### Example 2:  
+A DAO owes 100m FEI to the porter protocol. They have 30,000 stETH (at $2000/eth, 60m USD) as collateral in the porter protocol, and $70m liquid FEI in their treasury. 
+1. There is not enough FEI liquidity in Aave to take out a 30m FEI flash loan so the DAO takes out a 30m USDC flash loan
+2. DAO swaps 30m USDC for 30m FEI on a DEX
+3. DAO pays back their full 100m porter debt (which releases their collateral)
+4. DAO withdraws with their collateral and swaps some amount of it for 30m FEI on a DEX
+5. DAO repays Aave 30m FEI flash loan
+6. DAO now has their porter debt repaid and has their remaining collateral 
+
+
+[Aave flash loan example](https://github.com/aave/code-examples-protocol/tree/main/V2/Flash%20Loan%20-%20Batch)
+
+## Flash Loan alternatives considered
+Implementing flash loans in our protocol. 
+
+Example 3: \
+A DAO owes 100m DAI to the porter protocol. They have 10,000 stETH (at $2000/eth, 20m USD) as collateral in the porter protocol, and $90m liquid DAI in their treasury. 
+1. DAO withdraws their collateral
+2. DAO swaps some amount of the collateral for 10m DAI with a DEX
+3. DAO pays back their porter debt, which allows DAO to keep their collateral
+4. If they don't pay back the debt in the same transaction everything is reverted
+
+Pros: Avoid .09% aave fee \
+Cons: Would need to add flash loan logic to our protocol vs leveraging an existing one