* spec update: metadata keys are lowercase
* add batch parameter to metadata batches
* fix: connecting clients receive METADATA, not RPL_KEYVALUE
* spec update: send RPL_METADATASUBS in a metadata-subs batch
* move some helpers
* bump irctest to forked hash
This is https://github.com/progval/irctest/pull/314 but I don't want to
couple the merges
* fix: empty value is valid
* fix: deleting a nonexistent key gets a FAIL
* metadata spec update: disallow colon entirely
* refactor key validation
* implement metadata before-connect
* play the metadata in reg burst to all clients with the cap
* bump irctest
* remove all case normalization for keys
From spec discussion, we will most likely either require keys to be lowercase,
or else treat them as case-opaque, similar to message tag keys.
* refactoring
* send an empty batch if necessary, as per spec
* don't broadcast no-op updates
* don't trim spaces before validating the key
* bump irctest to cover metadata
* replay existing metadata to reattaching always-on clients
* use canonicalized name everywhere
* use utils.SafeErrorParam in FAIL lines
* validate key names for sub
* fix error for METADATA CLEAR
* max-keys is enforced for channels as well
* remove unlimited configurations
* maintain the limit exactly without off-by-one cases
* add final channel registration check
