Resolving watcher input IPLD blocks

[ashwinphatak]

• Watchers are state machines which take IPLD blocks as input and generate IPLD blocks and "watcher blocks" (which are identical to a Blockchain's) as output. There is a "mapper" which does arbitrary transformations on the input and are written in typescript.
• Watcher code is turing complete, so it's difficult to determine what subset of an input Ethereum block it's using in computing the derived state.
• Watchers can also perform eth_calls to compute derived state, resulting in usage of Ethereum state/storage created over an arbitrary no. of previous Ethereum blocks.
• Watchers are composable, so one watcher can use the data created by another.