Helper function to add history entries as tab completions

[krig]

Adds function which makes it easy to add the history as tab completions.

Usage example:

void completion(const char* buf, linenoiseCompletions* lc) { linenoiseAddHistoryCompletions(buf, lc); }

[rain-1]

Merged https://github.com/rain-1/linenoise/commit/53c5a1c60ed6c0657706cc4ff461f2070a914e53