docs/libcurl: minor cleanups

docs/libcurl: minor cleanups

I was reading curl_unescape(3) and I noticed that there was an extra
space after the open parenthesis in the SYNOPSIS; I removed the extra
space.

I also ran a few  grep -r  commands to find and remove extra spaces
after '(' in other files, and to find and replace uses of `T*' instead
of `T *'. Some of the instances of `T*` where unnecessary casts that I
removed.

I also fixed a comment that was misaligned in CURLMOPT_SOCKETFUNCTION.3.

And I fixed some formatting inconsistencies: in curl_unescape(3), all
function parameter were mentioned with bold text except length, that was
mentioned as 'length'; and, in curl_easy_unescape(3), all parameters
were mentioned in bold text except url that was italicised. Now they are
all mentioned in bold.
Documentation is not very consistent in how function parameter are
formatted: many pages italicise them, and others display them in bold
text; but I think it makes sense to at least be consistent with
formatting within the same page.

Closes #11027