v0.3.0

• Implemented content system, where you can define external HTML elements as something located on the map, with a possibility to tie it to a specific tile or another content object. These too use the mutation system, so you can store data related to them in Elemap.
• Creating grid map doesn't result in tiles automatically being added to it anymore.
• Tiles and rows are not required to be strictly sequential anymore, storage and rendering of tiles with arbitrary coordinates is now fully supported.
• Added createTile and createTiles grid methods, allowing to add tiles on the fly.
• Removed size from map arguments as grid no longer has a fixed size nor creates tiles during the initiation.
• Renamed orthogonal coords to carthesian.
• Renamed mutables to mutations.
• Grid tiles are now stored in a custom SignedArray object instead of plain array, with carthesian coordinates used as indices.
• Removed tileByIndex method and replaced all the instances of accessing tiles by indices with carthesian coordinates.
• tileByCoords method now takes either coords object or a [col, row] array. Hexagon map supports both axial and carthesian coords, but the array argument will always be converted to coords that are native to the map.
• Hexagon tile HTML elements now have attributes with both axial and carthesian coordinates.
• Map container HTML element is now saved between re-renders so it's not necessary to specify it every time after the first one.
• Outer tile HTML elements now use absolute positioning inside the row.
• Row HTML elements now use absolute positioning inside the grid.
• Adjusted indentation and recess systems to work with absolute positioning of tile HTML elements.
• Row HTML element width and grid HTML element height are now computed based on tile HTML element size data instead of using CSS max-content width due to migration to absolute positioning.
• CSS of default tile style of a grid is computed by applying it to a special invisible tile HTML element called mannequin instead of a tile with zero indices.
• Index classes are now defined in separate files.
• Fixed column and row coordinates being swapped all around the code.
• Fixed every render creating new style HTML elements instead of replacing innerHTML of the existing ones.
• Various small fixes and adjustments.