usually, there is always a sender around `getRecipient` call.
no need to recalculate sender. and more important, in some of
JSON-RPC/GraphQL call, the sender is come from `rpcCallData`,
not from `tx.getSender`. or in ohter situation when the tx is
an unsigned tx, without `r,s,v` fields to calculate sender.
- build all tools using the Makefile and place them in ./build
- add copyright header to Makefile
- premix/readme.md edited to fix some errors, improve descriptions and
document Makefile usage
- link the Premix documentation in the main README.md
- also build `hunter` in the nimble tests
- refactored the file and directory search so all debugging tools can be run
from the top-level dir like this: `./build/<tool> ...`
- write all JSON debugging data in the current directory
- add JSON files generated in the top-level dir to .gitignore
- Nimbus now exits with an exception after dumping debug data and
running `premix` on it