Minor POD modifications

[packy]

Looking over the POD, noticed three things:

• The constructor header shows up as "new HASHREF =head2 new URL, USERNAME, PASSWORD, REST_CLIENT_CONFIG, ANONYMOUS, PROXY, SSL_VERIFY_NONE"
• One of the constructor's arguments shows up as "username =item * password"
• The first paragraph of the constructor POD says "The [hashref] form [of the constructor] is preferred", but the sample code under "url" demonstrating how to specify a default API prefix still uses the positional argument form.

My spellchecker also flagged two typos for me, so I fixed them, too.

[gnustavo]

Thanks, @packy . These are all relevant. I'll rebase your commits just to reformat their comments to follow "my standards". ;-)

[gnustavo]

Rebased on next. These changes will be part of the next release. Thanks!