Source to Target alignment: reads source-target.A3.final files, in which each source word may be aligned to multiple target words (adapted from code by Sander Canisius)
Target to Source alignment: reads target-source.A3.final files, in which each source word is aligned to one target word
This class represent one document/text of the Corpus
This class represent one document/text of the Corpus, loaded into memory at once and retaining the full structure