Rewrite the cache store to match that done on impsort

[hazendaz]

Currently as discovered in a port attempt over to impsort, the cache was written, then closed, reopened, sorted, and removed the timestamp incorrectly after sorting instead of before. We need to do same here. See revelc/impsort-maven-plugin#90

[hazendaz]

Work is done and will be send in next day or two.