Fix conditional statement
Add support for arara

Arara is used as compiler if arara instructions are found in the source
file.
Modify inline command syntax

Inline commands now follow arara's format. For example, to set the
compiler, the following command is used:
        % rlatex: compiler: pdflatex
which replaces
        %rlatex: compiler pdflatex
The new syntax is consistent with arara's inline commands.