Changed structure of .pxo files

The structure of the .pxo files is now consisted of a JSON-structured metadata part, where all the data that can be stored as text are, and a binary part, that contain all the actual image data for each cel and project brush.

This makes it easier for users to understand the .pxo structure, easier to add more changes without having to check versions for backwards compatibility, easier to be opened by third-party apps and it allows us to make an "Export JSON metadata" option, that will export just the metadata in JSON format, without the binary image data.

It's backwards compatible and .pxo files from as far as v0.5 are still supported.

CHANGELOG.md

@@ -5,9 +5,15 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
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 ## [v0.8] - Unreleased
+This update has been brought to you by the contributions of:
+Darshan Phaldesai (luiq54)
 
 ### Added
 - Project tabs! You can now have multiple projects open at the same time, and access each one with tabs.
+- You can now draw on the tiling mode previews! ([#65](https://github.com/Orama-Interactive/Pixelorama/issues/65))
+
+### Changed
+- The .pxo file structure has been changed. It's now consisted of a JSON-structured metadata part, where all the data that can be stored as text are, and a binary part, that contain all the actual image data for each cel and project brush.
 <br><br>
 
 ## [v0.7.1] - Unreleased