Rework the mapping read and write APIs

[NebelNidas]

Changes

• MappingWriter implementations' methods are no longer static, use XyzWriter.getInstance() instead.
• MappingWriter#create(...) has been removed. Use format.newWriter(...) instead.
• MappingReader is now an interface. getNamespaces(...) and read(...) are no longer static.
  • Instead of the static MappingReader.read(path, format, visitor), use format.reader.read(path, visitor).
  • Instead of the static MappingReader.read(path, visitor), use MappingReader.detectFormat(path).reader.read(path, visitor).

Motivation

• Removing code duplication caused by MappingReader's static methods.
• Being able to check whether or not readers/writers actually exist for a given format without having to catch UnsupportedOperationException and IllegalStateException (see Calling MappingReader.read with an unsupported format results in an undescriptive exception #25).
• Removing implicit method calls, e.g. MappingReader.read(path, visitor) which called MappingReader.detectFormat(...) internally. This removal makes Use file extension for CSRG format detection #46 (comment) easier to implement and likely leads to consumers using more performant code paths now (since the less performant one is no longer shorter to type out).
• Having an instance for mapping writers allows for unifying the reader and writer changes in Add progress listeners #27.
• The API is now more closely aligned with other established mapping libraries like Enigma, Lorenz and SrgUtils.

Fixes #25.

[NebelNidas]

Needs further discussion.