Add support for multiline pica records.

The pica parser accepts new lines (\x0a) in the input as a field
delimiter. This makes it possible to parse not only pica plain but also
multi line pica records.

The test cases were refactored to make the input being tested more
visible.
Handles record markers in pica records gracefully (fixes #139).

Modified the pica parser to behave as if a field marker was encountered
when a record marker is encountered. Strictly speaking this is not
correct behaviour but the PicaDecoder expects single records in the
first place. Consequently a record marker should only be found at the
beginning or the end of the input.
Improved documentation of PicaDecoder.

Added an in-depth description of the parser behaviour.
Added header, footer and separator settings to ObjectWriter.

These settings allow to prefix the output with a header string and to
append a footer at the end of the stream. Additionally, the separator
between objects can be now changed. Previously, this was always a
newline character.

The default settings of header, footer and separator are chosen so that
the output of ObjectWriter is the same as in the old version of the
module (i.e. a new line character is append to each object).

In addition to these new options the encoding and compression options
can now be set via Flux.

This commit offers a solution for issue #152: The output of the JSON
encoder can be turned into a JSON array by setting header to "[",
separator to ", " and footer to "]".
Changed JsonEncoder to not prefix output with spaces.

Starting from the second object JsonEncoder added a space character to
each serialised object it generated (as pointed out in issue #152). This
commit changes the configuration of the JSON generator used by
JsonEncoder to not output these spaces.
Merge pull request #153 from cboehme/issue-152-additonal-writer-options

Solution for the issues described in #152
Merge pull request #141 from cboehme/multiline-pica-parser

Multiline pica parser