std/misc/vector

[fare]

Create a :std/misc/vector, with:

• variants of the vector-for-each, vector-map, vector-map!, vector-fold, vector-fold-right, and vector-count that behave like SRFI-43, but with different names that do NOT clash with R7RS and SRFI-133.
• import and adapt most of the code from gerbil-utils' :clan/vector.
• optionally, extra optimizations.
• documentation and tests

[fare]

Suggestion: vector-for-each/index (or maybe vector-for-each-indexed or vector-for-each-with-index.

[vyzo]

Let's consistently /index suffix.

[fare]

Fixed by #1046