all: bump to v0.14.0
xmpp: increase timeout on tests

This is still flakey in the VM, but I don't want to remove the timeout
entirely in case it blocks. If it hasn't finished in 10 seconds, even on
a slow VM, something else is going horribly wrong anyways so call it
good enough.
xmpp: fix bug where stream processing stops
internal/iter: don't mask close method
xmpp: don't count read timeouts as temporary
xmpp: factor out stream token handling
xmpp: move Negotiator into negotiator.go
all: update changelog
.github: experiment with sponsorship badge
all: add and use new internal/attr package

This finally removes all exported identifiers from the internal package
so that it doesn't turn into a junk drawer of functionality and
everything contains a name that's useful, not just a useless identifier
like "internal" that doesn't tell you anything about what the identifier

Update everything else to use the new package as well.
internal/stream: rename idents to reduce stutter

Also update usages.
internal/stream: new package for stream parsing

Also update all uses of old internal identifiers that were moved into
all: move stream namespaces into stream package
xmpp: make closing stream tag a const
all: gitignore .env and remove old Gopkg.toml line
internal/stream: use new decl package
internal/decl: new XML declaration package
examples/echobot: bump deps
stanza: don't require attributes on messages
xmpp: bump xmlstream to v0.13.6
roster: rewrite Iter in terms of internal iterator