Rename ZombieCharBuf to StackString (cnick SStr)
Rename CharBuf to String (cnick Str)
Whitespace fixes
Rename Clownfish::String tests
Initial implementation of CharBuf

Mostly copied from String.
Immutable versions of Str_Cat

These will be renamed later.
Convert Clownfish::Err to CharBuf
Convert TestUtils_random_string to CharBuf
Convert Clownfish::VTable to CharBuf
Eliminate Str_Cat_Char in SnowballStopFilter
Convert Highlighter to CharBuf
Use Str_Immutable_Cat for tempfile names.
Convert Index::DocVector to CharBuf