Changed the \includearticle command.

Problem: The current implementation forced the pdf file to be put in the root folder, and the file to be named identically to the citekey. This was implemented in the includearticle macro. The includearticle macro also forced centering withou alignment of the output from \fullcite. This is preferable for text in general on otherwise blank pages, but looked rather ill formatted for a citation.

This commit simply separates the argument of file path and citekey to two separate arguments in \includearticle. The optional pages parameter is also added to the README.md. This was undocumented before and is good. Often, papers have a cover page with metadata content from the publisher. To alleviate the output from \fullcite, this commit puts the citation in a flushleft environment for alignment. This means it is still centered, but left aligned.