Previously, int fields only accepted ints, and float fields only accepted floats. 
Now, these can be specified as strings, and will try to force convert to the correct type. 
Force conversion is done only when needed, to avoid large ints getting corrupted by converting to float and back to int. 

Fixes #99 and #108

…bbox'.

- Fixes issue in Py3 when converting text characters to byte strings, but in Py3 converts to unicode instead, because uses the Py2 specific str() function, instead of the version neutral b(). When the text contains non-ascii 2-byte unicode values this results in truncating the unicode length instead of the byte length, and thus results in incorrectly padded byte lengths and data values ending up in the wrong field/column. See #157, and also #148. 
- Also bump to next version.