ENH: cleanup Ostream to ease usage (issue #254)

- Include newline in beginBlock/endBlock, since this corresponds to
  the standard usage. The beginBlock now takes keyType instead of word.

- Provide Ostream::writeEntry method to reduce clutter and simplify
  writing of entries.

  Before
  ======
      os << indent << "name" << nl
         << indent << token::BEGIN_BLOCK << incrIndent << nl;
      os.writeKeyword("key1") << val1 << token::END_STATEMENT << nl;
      os.writeKeyword("key2") << val2 << token::END_STATEMENT << nl;
      os << decrIndent << indent << token::END_BLOCK << nl;

  After
  =====
      os.beginBlock("name");
      os.writeEntry("key1", val1);
      os.writeEntry("key2", val2);
      os.endBlock();

- For completeness, support inline use of various Ostream methods.
  For example,

      os << beginBlock;
      os.writeEntry("key1", val1);
      os.writeEntry("key2", val2);
      os << endBlock;

- For those who wish to write in long form, can also use endEntry inline:

      os.beginBlock("name");
      os.writeKeyword("key1") << val2 << endEntry;
      os.writeKeyword("key2") << val2 << endEntry;
      os.endBlock();

The endEntry encapsulates a semi-colon, newline combination.