Used default options for fetching as well as parsing

Allow installation alongside php-mf2 v0.5

* Default options are applied to calls to parse(), rels(), feeds() and process()
* Default options are overridden by options passed to the respective function call on a
  property-by-property basis
* Documented in README with example
* Added basic test (only for parse() behaviour)
* Also fixed a bug causing an error processing h-cards with no URL property

* Added isImgAlt static method to Formats\Mf2
* Used it in collectArrayURLValues and getPlaintext to handle cases where
  img+alt structures are encountered

Additionally disabled reporting of deprecation warnings while testing for
a cleaner output. All tests are passing.

Fix preg_replace deprecations

closes #105

closes #104

Updates to support php 8 anc CI

fix: check prefix correctly

The test is checking for notes, but 'Bridge Fed' is, in fact, an article according to the post discovery algorithm. Also, I'm adding as note that the main difference between a note and an article is that the latter has a title, while the first doesn't.

`strpos(string, sub)` returns `false` if `sub` is not present in `string`. In this case, we want to check if `sub` is not a *prefix* of `string`. Hence, we just need to test if the returned position is simply different from 0.

* looks through the full mf2 tree for step 7 of authorship https://github.com/indieweb/authorship/issues/2
* if no author h-card is found, falls back to returning the author URL without other data instead of missing author

closes #95

Allow iframe from YouTube and Vimeo

need to update htmlpurifier first

if the document contains a link to the target, but that link is not in the parsed result, don't return an error, but also don't return the parsed document

closes #150

for https://github.com/aaronpk/webmention.io/issues/150