Update to 1.2
New Settings "Anchor Label" and "Display URL"

Introduces two new features to this extensions:

 - Anchor Label: Adding an optional custom label for the links on the publish pages
 - Display URL: Display URL in entries table (Instead of anchor label)

See https://github.com/DeuxHuitHuit/link_preview/issues/3
Include entry ID by using the url format {$id}
Update extension.meta.xml to 1.2
Update README.md
Fixed typo
Introduced a new syntax for accessing system-data

To keep backwards-compatibility I didn't remove the old system-date-formatting.
So there are two methods to access system-dates right now:

**1) $system:variable**
Used for accessing the entry-id and system-dates "the old way"
 - $system:time
 - $system:date
 - $system:year
 - $system:id
 - ...

**2) $system:variable:qualifier**
Used as "the new syntax" to access system-dates. Follows the qualifier-concept used for the field-data and allows using all qualifiers for php date_format - e.g:
 - $system:date:d
 - $system:date:Y
 - $system:date:H:i
 - ...
Use a more Symphony-ish layout for the field's settings
Update README.md

Reflects the changes made to the syntax for formatting system-values as discussed here:

https://github.com/DeuxHuitHuit/link_preview/issues/5
https://github.com/DeuxHuitHuit/link_preview/pull/4
Fixed formatting

inluding `:date:` without code-formatting shows a github emoji ;)
Follow up of PR #4: UI adjustements

Make the two new inputs fields on two columns.
Some code refactoring.
Changing how we get the field id

This commit is a manual pick of 68025a4177ba5d53e161afe76fef88678e4a81a9.

> We now use the key of the array returned by $section->fetchFields();
Fix release date, author url and compatible versions
Some refactor to allow formats in the anchor label

This change refactors how string are formatted.
This change also reuses the code to format the anchor label.
markdown format
apply format on anchor label in publish page too
Added root, workspace and http-host system params

As per #8, those new params can be accessed usign
{$system:root}, {$system:workspace}, {system:http-host},
added doc about system params