* alternative flash lending (renting) design
* add rent interface
* fix stack too deep error
rearrange order of k condition math
ignore erroneous out of gas errors in tests
* try removing rent in favor of monolithic swap
IUniswapV2Borrower -> IUniswapV2Callee
update tests
* fix implementation
* clean up math a bit
* amount{0,1}In -> amount{0,1}InNet
* charge on all inputs, not just net
* removed unnecessary safemath
* add to != token check
don't indent in scope
rename reserve{0,1}Next -> reserve{0,1}Adjusted
* > instead of >=
simplify algebra
reserve{0,1}Adjusted -> balance{0,1}Adjusted
add comments
* add some optimistic swap test cases
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