leading spaces present inside pre tag when using format

[russell]

I think *suppress-inserted-spaces* t should be in effect by default when formatting a string in a pre so as to avoid adding leading spaces

this is very similar to #38

There is a leading space before the word foo

> (spinneret:with-html-string (:pre ("foo ~A" "for you")))
"<pre>
 foo for you</pre>"

where as with a normal string inside a pre there is no leading space

> (spinneret:with-html-string (:pre "foo" #\Newline "b" "a" "r"))
"<pre>foo
bar</pre>"