Added NPE handling to all expression stuff.

Updated pom.xml and plugin.yml (I always forget about them)

• Added "Body of document" expression
• Added "Head of document" expression
• Added "Title of document" expression
• Added "Inner/outer html of element" expression

Well, I love documents 😄

This update is a good one, promise me.

• Added option to set user agent in request document effect (You need to set both timeout and referer to use it!)

• Added some converters
  htmldocument to string
  htmlelement to string

• Changed how "text of htmlelement" works, it won't take child element texts now.

Some bug fixes
Added new expressions

• [the] [html] text of %htmlelement%

Thanks to
@WheezyGold7931 for fixing the static abuse

Skraper's first pre-release. Not trash :)