Provide has() method to Document
test: Set a default timezone if needed

The default timezone is set in the global PHP
configuration file, so it's not related to the
tests.

Should fix #22
Add simple tests for has() method
Merge branch 'has_field'

* has_field:
  Add simple tests for has() method
  Provide has() method to Document

Conflicts:
	tests/Prismic/DocumentTest.php
Build <img> tag programmatically
Add alt and copyright fields to images in test JSON, as per #23
Store and expose image alt and copyright info
Include image alt in markup
Add ImageView tests
Add SearchForm::count method
Make getBoolean case-insensitive
Accept array of override attributes on ImageView asHtml
Add case-insensitive getBoolean tests
Merge pull request #23 from tremby/feature/image-ashtml-improvements

ImageView improvements
Merge pull request #27 from tremby/feature/getboolean-improvements

getBoolean improvements
Turn newline characters into br tags in HTML, except in pre
Use multibyte substr and strlen functions

Fixes spans being positioned incorrectly after multibyte characters
Rewrite StructuredText::asHtmlText

This rewrite uses DOMDocument rather than manually editing the HTML
string.

We drill down to the right text node based on the required offset of
the span, split it in the necessary places and wrap it in the new
node. We then don't need to worry about the new tags causing offset
changes, since the DOM model doesn't count the tags as text.

It should be much more reliable; it's certainly much easier to read
and understand, in my opinion.

This patch also closes a couple of potential issues and one definite
issue: we skip over spans which are invalid (either improperly nested
or which end before they start).

There are commented out `throw new \Exception` lines where warnings
could be emitted. I don't want to throw exceptions because I still
want some rendered HTML.
Merge pull request #29 from tremby/feature/nl2br

Turn newline characters into br tags in HTML, except in pre
Merge pull request #36 from tremby/bugfix/handle-multibyte-characters

Use multibyte substr and strlen functions