v0.3.0

Added a bunch of options and squashed some bugs:

• Custom page-source definable
• id definable
• class definable in Kirbytag
• cols & mobilecols definable in Kirbytag
• Reworked stretch property and made it definable in Kirbytag
• Added all keyword to include all images on a page
• Added order option for optional random or reverse sorting
• Fixed a bug when stretch was set to false and count < cols