fix file IO flaw + CI fixes (#7)

There was a suble bug in reading files, due to not using io.ReadFull, but instead doing partial reads. This wasn't found in the tests, due to them only handling small files. The root issue has been fixed, aswell as better tests which hit the issue.

* ci: fixes for circle-ci config on v2
* fix error with file reading/writing, where non-full reads caused corruption

v2 module support

BACKWARDS INCOMPATIBLE: version update + json marshalling (#5)

* go modules support

* minor refactorings

* update binary format, fix text marshalling

* implement json marshalling/unmarshalling

* remove text marshaller interface

* remove debug, remove gob file

* Add .circleci/config.yml

* circle-ci config

* lint nitpicks

* readme: circleci badge

fix compile-flaw

marshaller: fix subtle size-bug