Issue #13 FoxPro memo field bugfix (#14)

* #13 - fix fox pro memo loading

* #13 add throw annotations, doc etc

* #13 foxpro write

* #13 fix

* #13 fix travis

* #13 fix

* #13 fix

* #13 fix

* #13 disable travis php 7.3

fixed Numeric field fraction handling

format

cast

empty fields

rename + tests

- fixed issue #6: problem when loading Visual FoxPro DBF

- updated travis.ci build matrix

- fixed PHP 7.2 related problems

- updated documentation

- added custom autoloader
- fixed finding memo files by extension incasesensitively
- fixes travis ci configuration

First release

 - support for dbase II format
 - ability to read / write / delete records
 - support for transactions
 - php7 compatible
 - table builder for creating new tables