Parsing synonym files

Elasticsearch will use the token filters preceding the synonym filter in a tokenizer chain to parse the entries in a synonym file. So, for example, if a synonym filter is placed after a stemmer, then the stemmer will also be applied to the synonym entries. Because entries in the synonym map cannot have stacked positions, some token filters may cause issues here. Token filters that produce multiple versions of a token may choose which version of the token to emit when parsing synonyms, e.g. asciifolding will only produce the folded version of the token. Others, e.g. multiplexer, word_delimiter_graph or ngram will throw an error.