Rename Tokenizer to BasicTokenizer.  Make several functions virtual.
Fixed some bugs on MemoryMappedList and SegmentedList
Merge branch 'PullFeatures' of https://github.com/chrisparnin/natix into chrisparnin-PullFeatures

Conflicts:
	natix.InformationRetrieval/Parsers/BasicTokenizer.cs
	natix.InformationRetrieval/Parsers/TextParser.cs
	natix.InformationRetrieval/SeqTextIR.cs
	natix.InformationRetrieval/natix.InformationRetrieval.csproj
merge is now OK