Add layer id parsing

Add support for multiline string properties

Fix markdown formatting in CONTRIBUTORS file

update Zstd to 0.9

Reorganize crate

Closes #99. ldtk seems to output tiled files with no newlines in the csv
data. Tiled itself does always seem to put the newlines in however, it
can open the ldtk files so we should too.

Implement Display for Orientation

Document that map dimensions are in tiles

And not, for example, in pixels

So that it can be more easily displayed to the user if needed

Add support for file properties

Add support for layer offsets

Feature-gate zstd so we can target wasm32-unknown-unknown

Object visibility needs parsed string, too

Layer and ObjectGroup are parsing "visible" string, but not object.
TMX docs indicate expected to be "0" or "1"
https://doc.mapeditor.org/en/stable/reference/tmx-map-format/#object

Add support for Infinite map

add support for base64/zstd

Add ObjectShape::Point for object layer

Fix deprecated methods in Error

add infinite map