always include long table

always include longtable
always include graphics

improved redefinition of include graphics such that it still can be used with options. This is to allow specific includegraphics embedded in markdown.

If one provides a latex stuff by --include-before-body or --include-after-body he should have the ability to provide tables and graphics there.

redefinition of includegraphics should not diminish the features of includegraphics if used in latex file directly or embedded in markdown.