Fix leading slash issue in relative URL requests

[aryan-25]

Motivation:

• When the leading slash is omitted in the string argument of a relative URL instance constructed from init(string:relativeTo), requests made with this URL instance fail. This is because the underlying HTTP parser fails when there is no leading slash in the URI.

Modifications:

• The URI of a URL instance is obtained from a computed property uri in HTTPHandler.swift, which in turn calls the percentEncodedPath computed property.
  • The percentEncodedPath property uses URLComponents to extract out the path.
  • The resolvingAgainstBaseURL argument to the URLComponents constructor was modified from false to true

Result:

• Regardless of whether a user provides or omits a leading slash in the path of a relative URL, the uri property will always contain a leading slash.

[fabianfett]

Looks great. Please compare against static absolute values in tests.

[fabianfett]

LGTM! Thank you!