Fix ZSTD_estimate* and ZSTD_initCStream() docs

Fix ZSTD_estimate* and ZSTD_initCStream() docs

Fix the following documentation bugs:
* Note that `ZSTD_estimate*` functions are not compatible with the external matchfinder API
* Note that `ZSTD_estimateCStreamSize_usingCCtxParams()` is not compatible with `nbWorkers >= 1`
* Remove incorrect warning that the legacy streaming API is incompatible with advanced parameters and/or dictionary compression
* Note that `ZSTD_initCStream()` is incompatible with dictionary compression
* Warn that