Re-implemented PicaDecoder based on a state machine.

The old PicaDecoder used regular expressions to parse PICA+ records. 
This let to two problems:

 * Errors in the data resulted in exceptions which did not refer to the    
   portion of the data that caused the problem (e.g. a character index)
 * Due to the use of String.substring() for extracting data from the  
   record the full record was kept in memory (see issue #51)

The new PicaDecoder was written to solve these problems. The first one
was addressed by constructing the parser so that it only fails in two
clearly defined situations (missing id field and unexpected end of
record). The second one was solved by copying the parsed data portions
into new strings. 

In addition to the problems listed above, the following issues were
addressed:
 
 * #109 -- removed support for static usages of the encoder
 * #112 -- removed support for appendControlSubField. If Metamorph is  
   extended to pass data through (issue #107), this functionality can
   easily be implemented in a script. It is also not clear how widely it
   is used at all.
 
While having removed support for control subfields the new decoder
introduces a range of new options:

 * ignore missing id -- do not fail on missing ids but use an empty 
   string as record id
 * skip empty fields -- do not output fields without subfields or empty
   subfields only (i.e. subfields without name and value)
 * fix unexpected end of record -- if a record does not end with a field 
   delimiter one will be automatically added.
 * normalize UTF8 -- automatically performs UTF8 normalization of values
 
The unit tests have been rewritten to match the new options and to be
more useful for debugging.