Improve dt- parsing

[gRegorLove]

• Do not add "T" separator if it's not in the authored HTML.
• Normalize timezone offsets to remove colons
• Imply timezone offset if included in another dt- in the same microformat (vcp: imply dates should also imply tz if needed microformats2-parsing#4)

Fixes #115 and #126

[aaronpk]

Why the added ? here? That makes the T optional. Should this instead be checking for a as well as T?

[gRegorLove]

Updated to [ T]

[aaronpk]

This should match Z OR +00:00, so probably a better regex would be

/(Z|[+-]\d{2}:?\d{2})/

[gRegorLove]

Since the timezone may also only be hours, updated this to /^(Z|[+-]\d{2}:?(\d{2})?)$/

[aaronpk]

What's the reason for making the minutes part optional here? It looks like the change is adding the ? to the minutes part of the timezone offset. Like the above, this should probably be changed to (Z|[+-]\d{2}:?\d{2})

I know this wasn't your change, but [a|p] and [+|-] is incorrect, since the regex is using [] you only need [ap] and [+-].

[gRegorLove]

Hour-only timezone offsets (+XX, -XX) are valid according to the VCP spec. I updated the am/pm regex in both locations to handle optional periods as well [ap]\.?m\.?

Edit: Re-reading, hour-only timezone offsets appear to only be valid if they appear in their own VCP element, separate from the time. Not sure if that's an oversight in the time+timezone section or not.

[aaronpk]

Do you need to match the colon here as well?

/[+-]\d{2}:?\d{2}/

[gRegorLove]

This is after the new method normalizeTimezoneOffset() is called, which removes the colon. This isn't explicitly stated in the spec, but I inferred it from: (bold is my emphasis)

However the colons ":" separating the hours and minutes of any timezone offset are optional and discouraged in order to make it less likely that a timezone offset will be confused for a time.

[gRegorLove]

@aaronpk Updated.the regexes and TZ normalization. Can you review?