docs: Rename `StartTime()` StreamOptFn to `StreamStartTime()`

[jrodewig]

IMPORTANT: Don't merge until https://github.com/fauna/fauna-go/pull/185 is merged.

Description

• Renames the StartTime() StreamOptFn to StreamStartTime() in the README to align with https://github.com/fauna/fauna-go/pull/185.
• Removes unneeded fauna. prefixes from several type and methods.

Motivation and context

Keep the docs up-to-date.

How was the change tested?

N/A

Screenshots (if appropriate):

Change types

• • [ ] Bug fix (non-breaking change that fixes an issue)
• • [ ] New feature (non-breaking change that adds functionality)
• • [ ] Breaking change (backwards-incompatible fix or feature)

Checklist:

• • [ ] My code follows the code style of this project.
• • [ ] My change requires a change to Fauna documentation.
• • [x] My change requires a change to the README, and I have updated it accordingly.

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