Update vinyl terminology in intro

[kostja]

https://tarantool.org/doc/intro.html:

Tarantool's disk-based storage engine is a fusion of ideas from modern filesystems, log-structured merge trees and classical B-trees. All data is organized into runs. Each run is represented by a file on disk. Run size is a configuration option and normally is around 64MB. Each run is a collection of pages, serving different purposes. Pages in a fully merged run contain non-overlapping ranges of keys. A run can be partially merged if there were a lot of changes in its key range recently. In that case some pages represent new keys and values in the run. The disk-based storage engine is append only: new data never overwrites old data. The disk-based storage engine is named vinyl.

We actually use the word "range" now for this. So, s/run/range/ in this paragraph.

On the same token, it's better to move and split this paragraph:

Tarantool supports multi-part index keys. The possible index types are HASH, TREE, BITSET, and RTREE.
To notimply that vinyl supports HASH, BITSET or RTREE.