monkey patching vanderlee/php-sentence#/27

use a k-means based cluster approach to speed up similarity searches

parse answers as markdown

removed K-D Tree vector storage

Since this implementation does not have any advantages over the SQLite
storage it makes no sense to keep it. Other storage backends might come
though at a later time

More robustness in creating the index

Retry failed API connections, do not abort the whole indexing and rather
skip a chunk. CLI testing tool for the split mechanism

pin php to 8.1

initial checkin. working vector storage and similarity search