[doc] docstring on indent function
[mod] variable renaming
[enh] new EndlProxyList (empty for now), put it on WhileNode
[enh] test EndlProxyList.__len__
[enh] code simple EndlProxyList.insert
[mod] update TODO
[enh] do EndlProxyList.insert work on inserting at the end
[mod] commit hidden tests todo