This change adds a test framework for the "eth" protocol and some basic
tests. The tests can be run using the './devp2p rlpx eth-test' command.

This change moves the RLPx protocol implementation into a separate package,
p2p/rlpx. The new package can be used to establish RLPx connections for
protocol testing purposes.
Co-authored-by: Felix Lange <fjl@twurst.com>

These commands mirror the key/URL generation functions of cmd/bootnode.

    $ devp2p key generate mynode.key
    $ devp2p key to-enode mynode.key -ip 203.0.113.21 -tcp 30304
    enode://78a7746089baf4b8615f54a5f0b67b22b1...

This adds an implementation of the current discovery v5 spec.

There is full integration with cmd/devp2p and enode.Iterator in this
version. In theory we could enable the new protocol as a replacement of
discovery v4 at any time. In practice, there will likely be a few more
changes to the spec and implementation before this can happen.

* log: delete RotatingFileHandler

We added this for the dashboard, which is gone now. The
handler never really worked well and had data race and file
handling issues.

* internal/debug: remove unused RotatingFileHandler setup code

* p2p/enode: add Iterator and associated utilities

* p2p/discover: add RandomNodes iterator

* p2p: dial using iterator

* cmd/devp2p: add discv4 crawler

* cmd/devp2p: WIP nodeset filter

* cmd/devp2p: fixup lesFilter

* core/forkid: add NewStaticFilter

* cmd/devp2p: make -eth-network filter actually work

* cmd/devp2p: improve crawl timestamp handling

* cmd/devp2p: fix typo

* p2p/enode: fix comment typos

* p2p/discover: fix comment typos

* p2p/discover: rename lookup.next to 'advance'

* p2p: lower discovery mixer timeout

* p2p/enode: implement dynamic FairMix timeouts

* cmd/devp2p: add ropsten support in -eth-network filter

* cmd/devp2p: tweak crawler log message

This adds an implementation of node discovery via DNS TXT records to the
go-ethereum library. The implementation doesn't match EIP-1459 exactly,
the main difference being that this implementation uses separate merkle
trees for tree links and ENRs. The EIP will be updated to match p2p/dnsdisc.

To maintain DNS trees, cmd/devp2p provides a frontend for the p2p/dnsdisc
library. The new 'dns' subcommands can be used to create, sign and deploy DNS
discovery trees.

* p2p/discover: export Ping and RequestENR

These two are useful for checking the status of a node.

* cmd/devp2p: add devp2p debug tool

This is a new tool for debugging p2p issues. It supports a few
basic tasks for now, but many more things can and will be added
in the near future.

   devp2p enrdump            -- prints ENRs readably
   devp2p discv4 ping        -- checks if a node is up
   devp2p discv4 requestenr  -- gets a node's record
   devp2p discv4 resolve     -- finds a node through the DHT

* add-date-to unstable

* fields-insteadof-split

* internal/build: support building with missing git

* docker: add git history back to support commit date in version

* internal/build: use PR commits hashes for PR builds

This change introduces 

    ethkey changepassphrase <keyfile>

to change the passphrase of a key file.

This commit:

- Adds a --msgfile option to read the message to sign from a file
  instead of command line argument.
- Adds a unit test for signing subcommands.
- Removes some weird whitespace in the code.

ethkey is a new tool that serves as a command line interface to
the basic key management functionalities of geth. It currently
supports:
 
 - generating keyfiles
 - inspecting keyfiles (print public and private key)
 - signing messages
 - verifying signed messages