Fix uri format to follow RFC 3986

[itchyny]

It seems that the current implementation is based on RFC 2396 - 2.3. Unreserved Characters. However, this RFC is obsoleted by RFC 3986. At RFC 3986 - 2.3. Unreserved Characters, the unreserved characters are defined as follows.

unreserved  = ALPHA / DIGIT / "-" / "." / "_" / "~"

Thus we should update the implementation to follow the RFC 3986.

 % echo "-_.~\!'()" | jq -R @uri
"-_.~!'()"
 % echo "-_.~\!'()" | ./jq  -R @uri
"-_.~%21%27%28%29"

Resolves #1506.

[coveralls]

Coverage increased (+0.4%) to 84.525% when pulling bafbe91 on itchyny:fix-uri-rfc3986 into a17dd32 on stedolan:master.

[itchyny]

Thank you.