lowerAscii and upperAscii are in tests but not specification

[allanlw]

The conformance tests contain tests for the lowerAscii and upperAscii functions, however these do not appear in the spec documentation. Interestingly the upperAscii function is referenced in another part of the doc though.

I found the following blurb in the README of cel-go here:

Returns a new string where all ASCII characters are lower-cased.

This function does not perform Unicode case-mapping for characters outside the
ASCII range.

     <string>.lowerAscii() -> <string>

Examples:

     'TacoCat'.lowerAscii()      // returns 'tacocat'
     'TacoCÆt Xii'.lowerAscii()  // returns 'tacocÆt xii'