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

Leave defaults for linking Boost libraries on non-WIN32. WIN32 atm needs to link to static libraries for some reason.

Looks like there's no conversion between const char* and string::const_iterator on MSVC (actually it sounds safer if you ask me). Anyway, working around that by wrapping const char* around a std::string

If SIGUSR1 is not defined, skip the code that registers handler for TokenTimer (so yes, it is not fully functional on a system without SIGUSR1).

Make add_library use default setting which is set to SHARED libs for anything but WIN32. WIN32 libs are going to be STATIC until external API is specifically defined (Windows' DLLs export nothing by default, UNIX shared libs export everything)