Release 6.1.2

prometheus_text_format: Fix argument order for `format_into/3` fun

The formatting function should take the state as the first argument and
new data as the second. See `format/1` which passes in the trailing
linefeed as the second argument. This doesn't make much difference when
calling `format/1` because the swapped arguments only caused the metrics
to be concatenated in reverse. But this fix is important for using
`format_into/3` correctly, for example with `cowboy_req:stream_body/3`.

prometheus_text_format: Eliminate `ram_file`, add `format_into/3`

Building on the work in the parent commit, now that the data being
passed to the `ram_file` is a binary, we can instead build the entire
output gradually within the process. We pay in terms of I/O overhead
from writing and then reading from the `ram_file` since `ram_file` is a
port - all data is passed between the VM and the port driver. The memory
consumed by a port driver is also invisible to the VM's allocator, so
large port driver resource usage should be avoided where possible.

Instead this change refactors the `registry_collect_callback` to fold
over collectors and build an accumulator. The `create_mf` callback's
return of `ok` forces us to store this rather than pass and return it.
So it's a little less hygienic but is more efficient than passing data
in/out of a port.

This also introduces a function `format_into/3` which can use this
folding function directly. This can be used to avoid collecting the
entire response in one binary. Instead the response can be streamed
with `cowboy_req:stream_body/3` for example.

Release v6.0.3

Release v6.0.2

Fix capturing new metric names (#191)

Fix documentation for quantile summaries

Release v5.1.1

Release v5.1.0

Release v5.0.0