Check for reverse prompt by characters instead of tokens (ggml-org#292) (ggml-org#330)

* Check for reverse prompt by characters instead of tokens (ggml-org#292)

* Update main.cpp

Wording.

* Cleanup.

* Remove unnecessary use of std::stringstream.

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Co-authored-by: Johnman <tjohnman@github>
Co-authored-by: Georgi Gerganov <[email protected]>

Author: 3 people