Implementation fixes for OLE string conversions.

* Remove 10,000 character limit on string-conversion functions by dynamically getting size of original string
* Split UTF16PtrToString into two separate functions, one for LPOLESTR's (LpOleStrToString)
and one for BSTR's (BstrToString), since some Windows/COM functions use one type or the other
* Keep UTF16PtrToString as an alias for LpOleStrToString, to keep ole package API compatible with previous versions
* Refactor library code to use either LpOleStrToString or BStrToString, as appropriate
Merge pull request #35 from mgspross/issue34

Implementation fixes for OLE string conversions. Closes #34