Proto commits in tikv/rust-prometheus

These 2 commits are when the Protocol Buffers files have changed:

Commit:89ca699
Author:Francis Lalonde
Committer:Ana Hobden

Make protobuf dependency optional (#216) * Make protobuf dependency optional * Remove many Option<> from no_proto * Apply formatting to no_proto * Remove unused import in tests * Fix tests with 'protobuf' feature disabled * Rename 'proto' module to 'model' & delete unused fn from 'plain_model' * Format changes using cargo fmt * Revert proto -> model module name change * Fix rustfmt::skip attribute

The documentation is generated from this commit.

Commit:9b908f2
Author:siddontang
Committer:Neil Shen

*: initialization. (#1)