feat(doc): add documentation to all public items

[joshuachp]

Add warning and documentation for missing doc comments on public items or modules.

Closes #257

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 0% with 1 lines in your changes are missing coverage. Please review.

Project coverage is 67.7%. Comparing base (26f8e7e) to head (183556c). Report is 1 commits behind head on master.

Additional details and impacted files

| [Files](https://app.codecov.io/gh/astarte-platform/astarte-device-sdk-rust/pull/315?dropdown=coverage&src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=astarte-platform) | Coverage Δ | | |---|---|---| | [src/aggregate.rs](https://app.codecov.io/gh/astarte-platform/astarte-device-sdk-rust/pull/315?src=pr&el=tree&filepath=src%2Faggregate.rs&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=astarte-platform#diff-c3JjL2FnZ3JlZ2F0ZS5ycw==) | `70.0% <ø> (ø)` | | | [src/connection.rs](https://app.codecov.io/gh/astarte-platform/astarte-device-sdk-rust/pull/315?src=pr&el=tree&filepath=src%2Fconnection.rs&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=astarte-platform#diff-c3JjL2Nvbm5lY3Rpb24ucnM=) | `63.7% <ø> (+0.6%)` | :arrow_up: | | [src/interface/def.rs](https://app.codecov.io/gh/astarte-platform/astarte-device-sdk-rust/pull/315?src=pr&el=tree&filepath=src%2Finterface%2Fdef.rs&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=astarte-platform#diff-c3JjL2ludGVyZmFjZS9kZWYucnM=) | `70.2% <ø> (ø)` | | | [src/interface/mapping/endpoint.rs](https://app.codecov.io/gh/astarte-platform/astarte-device-sdk-rust/pull/315?src=pr&el=tree&filepath=src%2Finterface%2Fmapping%2Fendpoint.rs&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=astarte-platform#diff-c3JjL2ludGVyZmFjZS9tYXBwaW5nL2VuZHBvaW50LnJz) | `65.8% <ø> (+2.5%)` | :arrow_up: | | [src/interface/mapping/path.rs](https://app.codecov.io/gh/astarte-platform/astarte-device-sdk-rust/pull/315?src=pr&el=tree&filepath=src%2Finterface%2Fmapping%2Fpath.rs&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=astarte-platform#diff-c3JjL2ludGVyZmFjZS9tYXBwaW5nL3BhdGgucnM=) | `61.8% <ø> (ø)` | | | [src/interface/mod.rs](https://app.codecov.io/gh/astarte-platform/astarte-device-sdk-rust/pull/315?src=pr&el=tree&filepath=src%2Finterface%2Fmod.rs&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=astarte-platform#diff-c3JjL2ludGVyZmFjZS9tb2QucnM=) | `77.3% <ø> (ø)` | | | [src/interface/reference.rs](https://app.codecov.io/gh/astarte-platform/astarte-device-sdk-rust/pull/315?src=pr&el=tree&filepath=src%2Finterface%2Freference.rs&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=astarte-platform#diff-c3JjL2ludGVyZmFjZS9yZWZlcmVuY2UucnM=) | `73.6% <ø> (+3.6%)` | :arrow_up: | | [src/introspection.rs](https://app.codecov.io/gh/astarte-platform/astarte-device-sdk-rust/pull/315?src=pr&el=tree&filepath=src%2Fintrospection.rs&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=astarte-platform#diff-c3JjL2ludHJvc3BlY3Rpb24ucnM=) | `100.0% <ø> (ø)` | | | [src/store/mod.rs](https://app.codecov.io/gh/astarte-platform/astarte-device-sdk-rust/pull/315?src=pr&el=tree&filepath=src%2Fstore%2Fmod.rs&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=astarte-platform#diff-c3JjL3N0b3JlL21vZC5ycw==) | `100.0% <ø> (ø)` | | | [src/transport/grpc/mod.rs](https://app.codecov.io/gh/astarte-platform/astarte-device-sdk-rust/pull/315?src=pr&el=tree&filepath=src%2Ftransport%2Fgrpc%2Fmod.rs&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=astarte-platform#diff-c3JjL3RyYW5zcG9ydC9ncnBjL21vZC5ycw==) | `60.7% <ø> (+0.5%)` | :arrow_up: | | ... and [5 more](https://app.codecov.io/gh/astarte-platform/astarte-device-sdk-rust/pull/315?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=astarte-platform) | | ... and [1 file with indirect coverage changes](https://app.codecov.io/gh/astarte-platform/astarte-device-sdk-rust/pull/315/indirect-changes?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=astarte-platform)

[joshuachp]

Added some periods to the end of the comments, not all, since it's not a priority and can be done gradually.