Various improvements, updated libraries and image features

[Emulator000]

In this PR I updated all libraries, applied various code improvements, fixed tests in case of non enabled chrono feature and done some enrichments on the embed_image feature, now supports buffers.

I also added an useful function for the Document struct called get_object_page(), this function will return the Page ObjectId if found, useful for inserting certain element of another dependent ObjectId and another useful remove_object() function that is able to correctly remove an object from the page and the reference.

I also formatted the code with cargo fmt in order to be compliant to all Rust 2018 rules.

@J-F-Liu please wait before merging this, I'll to check if the embed_image is working properly because I think that is a little buggy. Maybe is not well tested as is not a default feature :-)

[Emulator000]

@J-F-Liu you can now review and merge now!

I've fixed a failing test on the CI too, everything should be ok :)

Let me know when you will cargo publish it in order to immediately use it on my project, thank you!

[J-F-Liu]

Package version should be 0.26.0, or leave it unchanged, I'll bump the version number separately and publish.

[Emulator000]

@J-F-Liu done, changed to 0.26 :-)

Please let me know when you'll publish it, thanks!

[J-F-Liu]

Published just now.