adding null value handling in Writer class #28
remove constructor from abstract class
move encoding to ConverterTrait
Merge pull request #30 from thephpleague/nullvalue

adding null value handling in Writer class #28
bug fix null
Bump to version 5.3
adding null value handling in Writer class #28
bug fix null
Bump to version 5.3
Update NullHandling names
fix merge conflict
change property visibility for Writer::null_handling_mode
Merge branch 'master' into locale

Conflicts:
	README.md
	src/AbstractCsv.php
	src/ConverterTrait.php
	src/Iterator/IteratorFilter.php
	src/Iterator/IteratorInterval.php
	src/Iterator/IteratorQuery.php
	src/Iterator/IteratorSortBy.php
	src/Iterator/MapIterator.php
	src/Reader.php
	src/Writer.php
	test/WriterTest.php