Fix for ImageMagick 7+

[humphreyn]

fixes #29

Requires ImageMagick 7+

Enables the use of any of the following image engines:

• native
• graphicsMagick
• imageMagick

Enables setting of optional password for password encrypted or restricted PDF's. Added new tests for password encrypted and password restricted PDF's

Tested against:

• GraphicsMagick v1.3.35-Q8
• ImageMagick v7.1.0-Q16
• Ghostscript v9.52

[humphreyn]

Hi @marcdacz, sorry for the delay I have removed the linting and supplied a fix for using ImageMagick 7+.

You can also now use a password for encrypted pdf files and any of the image engines

[marcdacz]

thanks for raising the PR mate. would it be too much if I ask you to split this into 2? since it also includes the password option as well.

[humphreyn]

@marcdacz , ok will split into two PR's

[marcdacz]

@humphreyn is there any update on splitting these? I will decline this for now and will wait for your next PRs

[humphreyn]

Hi @marcdacz , Sorry for this work has been a nightmare. I will try and get this done over the weekend