FIX: removing last component deletes entity as well

[gretkierewicz]

fixes #82

Due to boy scout rule, there are additional minor changes:

• add more explicit exceptions
• change return to removed component instead of entity

[gretkierewicz]

@benmoran56 check this out pls

I'm using pop() instead of del to return removed component but it should not have big performance impact overall

[benmoran56]

I'll try to get a point release out soon.