Pre-Release 3.0.0a3

• Removed legacy error types from pygerber.gerber.api._errors.
• Removed pygerber.common.general_model module.
• Removed pygerber.common.immutable_map_model module.
• Removed pygerber.common.rgba module.
• Rename Project class from pygerber.gerber.api to CompositeView.
• Changed source_code and file_type attributes of GerberFile to be read-only.
• Changed return type of CompositeView.render_with_pillow to CompositePillowImage.
  Interface of CompositePillowImage is the same as previously CompositeView.
• Changed miniatures displayed by language server to be fixed size due to repeating
  problems with apertures being too small or too large.
• Added custom __str__ to CompositeView and GerberFile classes.
• Added GerberJobFile class for handling .gbrjob files.
• Added Project class for grouping multiple CompositeView objects.
• Added documentation for GerberJobFile and Project classes.
• Added pygerber.vm.shapely package containing implementation of Gerber vm (renderer)
  using shapely library.
• Added render_with_shapely to GerberFile class.
• Updated Quick start guide.
• Updated many of docstrings in pygerber.gerber.api package.
• Restored pygerber_language_server command.