SLIME 2.4 released

[Luís Oliveira]

Hello all,

SLIME 2.4 is released! https://github.com/slime/slime/releases/tag/v2.4

I've also updated the on-line HTML and PDF documentation and added a
link to the GitHub releases page to the website.

Cheers,

-- 
Luís Oliveira
http://kerno.org/~luis/