Added removeAttributes method - removing multiple attributes

[Machy8]

• bug fix? no
• new feature? yes

Description

• Added method removeAttributes for removing multiple attributes
• Why: for example when converting html element to the Amp html element, sometimes is necessary to remove multiple (by Amp disabled) attributes like frameborder, allowfullscreen or scrolling
• There is already a method for setting multiple attributes but non for removing multiple attributes so it means to create loops in order to remove them

[dg]

Thanks