feat(client): blocking LineSenderPool (#53)

Breaking change of an experimental API

The pool now blocks if there are already too many senders in use.
Pooled senders are released implicitly, via the Close call.

feat(client): add sender pool (#47)

Co-authored-by: Andrei Pechkurov <37772591+puzpuzpuz@users.noreply.github.com>

fix(client): fix request_min_throughput config parameter name (#43)

Also fixes godoc formatting for LineSenderFromConf

fix(client): fix auto_flush_interval units in LineSenderFromConf (#40)

fix(client): broken HTTP sender retries (#39)

fix(client): HTTP sender retries send empty request body (#38)

feat(client): add LineSenderFromEnv method (#35)

Also improves the docs around HTTP transport

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Co-authored-by: Andrey Pechkurov <apechkurov@gmail.com>

fix(config): enables optional trailing semicolon in config string (#32)

fix(client): Go 1.19 compatibility (#30)

fix(client): modify config parsing behavior to match other clients (#28)

Co-authored-by: Andrey Pechkurov <apechkurov@gmail.com>