updated with the new don't-encode-already-encoded-data concept

.SH DESCRIPTION

This function will convert the given input string to an URL encoded string and

return that as a new allocated string. All input characters that are not a-z,

A-Z or 0-9 will be converted to their "URL escaped" version.

A-Z or 0-9 will be converted to their "URL escaped" version. If a sequence of

%NN (where NN is a two-digit hexadecimal number) is found in the string to

encode, that 3-letter combination will be copied to the output unmodifed,

assuming that it is an already encoded piece of data.

If the 'length' argument is set to 0, curl_escape() will use strlen() on the

input 'url' string to find out the size.