Flowio

* Major reworking of create_fcs function to support writing files with log scale or gain metadata
* FCS keyword list available via fcs_keywords module
* Version now accessible via flowio.__version__
* BUGFIX: fix incorrect byte offsets in create_fcs when metadata contained 2-byte UTF-8 characters
* API: FlowData.write_fcs no longer takes separate extra & extra_non_standard args, unified to new metadata arg
* API: create_fcs arguments simplified, cyt, date, extra, extra_non_standard are merged into new metadata arg

BUGFIX: Fixes issue where data offsets were not set correctly when exporting large FCS files (issue 12). Thanks to andreas-wilm for PR 13.
BUGFIX: Export of FCS files would fail in rare cases where the text section byte length would be off due to the length increasing by one digit (leading to incorrect DATA section offset).
API: FlowData attribute `cur_offset` is no longer public (is only used internally in the constructor)

Added optional argument `only_text` to FlowData constructor to only read the "text" segment of FCS files without loading event data. This allows faster parsing of a large number of files to inspect metadata, and also uses less memory.

Thanks to JcGKitten for the feature request & implementation (pull request 11)

Significantly improves read times for FCS files.

This release updates documentation and adds an error when parsing FCS files where the data offset is reported incorrectly. Some FCS files incorrectly report a data offset that is off by 1 byte yet the file is not corrupt. For this case, the new FlowData option `ignore_offset_error` can be set to True to force reading in these files.

This version drops support for Python 2 (0.9.9 is the last version that is compatible with Python 2).

BUGFIX: fixes issue parsing FCS files with mixed integer bit sizes for events in different channels (issue 9)

ACKNOWLEDGEMENTS:

Thanks again to matt-faria for reporting the issue and submitting PR 9