feat: Convert <boolean> values to <c-long> values

Maps <boolean> parameters to <integer> where curl functions interpret
0 as #f and 1 as #t.

Introduce <curl-boolean> mapped subtype and <curlopt-boolean> so now,
for instance the option 'verbose' can be declared as:

  define curlopt boolean verbose = 41;

and the dylan code to use it is:

  curl.curl-verbose := #t;

Closes #1

Author: fraya