version bump 0.7.2: pre-BIFF5 support

- allow for naked streams (pre-BIFF5, CFB optional)
- support pre-BIFF5 strings and widths
- removed nested functions in parse_xlscfb, added more record types
- README improvements (paralleling js-xlsx)
- fake "Sheet1" name if sheet name is missing (fixes #57, h/t @egon12)
- demo only processes one file (addresses #52)
- updated CFB (bits/18_cfb.js pulled from js-cfb)
- cellStyles option (only supports patternType)
- sheet_to_json __rowNum__ now non-enumerable (h/t @SystemParadox)
- strip sourceMappingURL references from minified scripts (h/t @vinin3)
- sheet_to_json header === 1 now includes empty rows (h/t @tamlyn)

Related:

https://github.com/SheetJS/js-xlsx/issues/139
https://github.com/SheetJS/js-xlsx/issues/142
https://github.com/SheetJS/js-xls/issues/51
https://github.com/SheetJS/j/issues/8