update AnnotationChannel interface, fix make_iob_from_segments bug, upgrade make_annotation_vector, annotation heads

ignore consecutive colons in tag parsing, so parsing 'subst::::' throws an attribute-missing error instead of a unknown-value

initial switch to use shared_ptrs for sentence and chunk objects, ale get rid of the pointless sentence template

That should finally solve the issues of static vs dynamic libraries
conflicts that were arising when we tried to dynamically link boost
DLLs but didn't do anything about auto-linking feature that
wanted to link static libs.
ATM I left the default static linking on due to some warnings about
using non-DLL interfaced classes in classes that have DLL interfaces.

use the msvc-compatible string() casts instead of the working on gcc, but probably noncompliant, char* to itertor casts