Update reference.md

Fix problem with ’ in section "e" under "String functions"
Update index.rhtml

Added link to Danish translation.
Update index.rhtml

Alphabetic sorting of other languages, keeping outdated last in the list.
Update doc.md

Changes 'css' and 'less' to uppercase if not part of file name.
Update usage.md

Changes 'css' and 'less' to uppercase if not part of file name.
Info on removal of  as a breaking change. Credit to the 'less core team'