Assertion subject (obj) changes when using ownProperty assertion

[lucasfcosta]

This aims to solve #281.
I've finished the changes to the assertion implementation but I also plan to add this assertion to the assert interface (and add tests for that).

• ownProperty JSDoc Comments (Examples included)
• ownProperty accepts value
• ownProperty changes target (enables chaining)
• ownProperty tests on should interface
• ownProperty tests on expect interface
• Implementation on the assert interface
• ownProperty tests on assert interface

[keithamus]

Everything about this looks great so far. Look forwarding to seeing a complete PR @lucasfcosta 😄

[lucasfcosta]

Well, I think it's done.
Thanks for taking a look at it @keithamus, I hope you like this 😄

[keithamus]

Stellar work as always @lucasfcosta!

[lucasfcosta]

Thanks!
Let's keep pushing Chai forward 😄