Fix a couple of memory leaks in AXSH_InitEngineState() error handling.
AXSH_TclActiveScriptSite: Replace init function with constructor-like function.

* new function AXSH_CreateTclActiveScriptSite() allocates memory, sets the
    reference counter to 1 and returns the pointer to the object
* the Release() mechanism is used when the object is not used anymore
* use CoTaskMemAlloc() / CoTaskMemFree() instead of malloc() / free()
Change TclHostControl memory management, fix IActiveScriptSite::GetItemInfo().

* AXSH_TclActiveScriptSite: Fix missing AddRef() calls when returning
    interface pointers from GetItemInfo() method
* thus the new call to TclHostControl's Release() in AXSH_CleanupEngineState()
* new function (constructor-like) function AXSH_CreateTclHostControl()
    allocates memory, sets the reference counter to 1 and returns the pointer
    to the object - this replaces AXSH_InitHostControl()
* AXSH_TclHostControl structure: rename pVtableTypeInfo to pInterfaceTypeInfo
* use CoTaskMemAlloc() / CoTaskMemFree() for TclHostControl object
* TODO comments (cleanup old ones, add new ones)
* rename CLSID_ITclHostControl to CLSID_TclHostControl (as in .idl file)
* normalize names of cleanup goto labels