Simplified some functions in tstring.cpp by replacing with standard functions.
Added UTF-8 check when constructing a String from a char.
Removed some redundant code from tsmartptr.h.
Fixed some misspellings.
Added a missing test for ByteVector::toFloat80().
Fixed a wrong conversion in ByteVector::toFloat64BE().
Merge pull request #373 from TsudaKageyu/snprintf-spelling

Fixed some misspellings.
Merge pull request #363 from TsudaKageyu/string-std-func

Simplified some functions in tstring.cpp by replacing with standard func...
Merge pull request #374 from TsudaKageyu/redundant-smartptr

Removed some redundant code from tsmartptr.h.
Merge pull request #376 from TsudaKageyu/test-float80

Added a missing test for ByteVector::toFloat80().