- relax casting rules
  * down-cast of labelToken to boolToken
  * up-cast of wordToken to stringToken.
    Can use isStringType() test for word or string types

- simplify constructors, move construct etc.

- expose reset() method as public, which resets to UNDEFINED and
  clears allocated storage etc.

DEFEATURE: remove assign from word or string pointer.

- This was deprecated 2017-11 and now removed.
  For this type of content transfer, move assignment should be used
  instead of stealing pointers.

- creates a std::string with space-delimited tokens, which can be sent
  to another application or even re-parsed into tokens

- symmetric with writeRaw() etc for the output stream. These are
  methods that are not required by normal users, but which provide
  a finer granularity for reading.

- additional information about the current stream position when
  endList fails. This may help when tracing errors.

STYLE: change return type of beginRaw()/endRaw() to bool

- was of type Ostream& for output, but return value was unused.
  Having bool may be better for encapsulating logic

STYLE: remove unused Istream::readEndBegin() function

- a failed attempt to read a value (eg, word, label, scalar) from a
  stream now always provokes a FatalIOError.
  This helps avoid some difficult to trace input errors.

- simplify string output code

- for convenience and symmetry with OStringStream

STYLE: void return value for stream rewind() methods

- this makes it easier to design bidirectional streams

Avoids the clutter and maintenance effort associated with providing the
function signature string.

The new NotImplemented macro uses __PRETTY_FUNCTION__ for GNU compatible
compilers otherwise __func__ to provide the function name string.

This reverts commit c5bea524.

This reverts commit b18f6cc1.

- The lineNumber of token::undefinedToken was being changed instead of
  just the lineNumber of the return token.

- use List::first() and List::last() methods as well

- Istream and Ostream now retain backslashes when reading/writing strings.
  The previous implementation simply discarded them, except when used to
  escape a double-quote or a newline. It is now vitally important to retain
  them, eg for quoting regular expression meta-characters.

  The backslash continues to be used as an escape character for double-quote
  and newline, but otherwise get passed through "as-is" without any other
  special meaning (ie, they are *NOT* C-style strings). This helps avoid
  'backslash hell'!
  For example,
     string:   "match real dots \.+, question mark \? or any char .*"
     C-style:  "match real dots \\.+, question mark \\? or any char .*"

- combined subfiles in db/IOstreams, some had more copyright info than code
- OPstreamI.H contained only private methods, moved into OPstream.C

Are these really correct?
   IOstreams/Istream.H:#   include "HashTable.C"
   token/token.H:#define NoHashTableC