Add endpoint to fetch year-based match counts by ngram text

[mtrenkmann]

Fetching year-based match counts is currently a two-step process:

1. Send a search request and get a list of matching lite ngrams (including ngram IDs).
2. Send an ngram ID in an ngram request and get the corresponding full ngram with year-based stats.

This feature request proposes to support this use case in a one-step process by introducing a new endpoint like:

GET {base_url}/{corpus}/get?ngram={ngram_text}&flags={flags}

• The response is a full ngram.
• The lookup is case-sensitive.
• Supported flags are ri, rn, rt, ra, see flags.