1. Convert to using re module

2. Added two new exception classes

    a. MissingSectionHeaderError which signals an early parsing
       exception when options appear in the file before any section
       header.  Previously a bogus TypeError was thrown deeper down.

    b. ParsingError which collates any non-fatal parsing errors.
       ConfigParser.read() will raise this after the entire file was
       parsed if any errors occurred during parsing (client could just
       catch the exception and continue, because the ConfigParser
       instance would still be initialized with the valid data).

   (small note: Error.__msg => Error._msg)

3. ConfigParser.__read() now uses re which has the following minor
   semantic change: underscore is now allowed in section header and
   option name.  Also, because of the old regexps, theoretically.
   Fixed continuation line bug reported by F. Lundh.

4. It seemed that the old ConfigParser automatically added the option
   `name' to every section, which contained the name of the section.
   This seemed bogus to me so I took it out.