Do not generate atoms / custom metrics formatting

[aerosol]

Hello,

This PR introduces two changes:

1. All the names are now transferred as list of binaries, instead of generating atoms at runtime. This is useful for an environment where metrics are built dynamically, preventing the VM from exploding due to atoms not being garbage collected. exometer is perfectly fine accepting lists of terms for metric identifiers.

2. New configuration options:

• max_messages - allows fine tuning the pobox buffer size
• formatter - allows injecting a custom metric name formatting function, useful for legacy systems where metrics have already a naming scheme that needs to be preserved.

Let me know please, if this is good to go 🍻

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[sourcelevel-bot]

Ebert has finished reviewing this Pull Request and has found:

• 1 fixed issue! 🎉

You can see more details about this review at https://ebertapp.io/github/pinterest/elixometer/pulls/74.

[jparise]

This looks great to me. Thanks!

Let's see if @scohen has any comments before we merge.

[scohen]

@jparise my only concern here is that pre-existing metrics will somehow have their names changed, though I'm skeptical that this will be the case, since the stringified version of an atom is just the atom.

[scohen]

Will this still work for metrics defined as an atom list?

[jparise]

Either way, lets cover that case with a test.

[aerosol]

7061c28 - is that what you meant?

[jparise]

Thanks for the contribution, @aerosol!