Description of the PR

Added CORE output generator for generating XML files in CORE's format

closing #22

Review checklist

(based on the work of Karl E. Wiegers)

Structure

[x] Does the code completely and correctly implement the design?
[x] Is the code well-structured, consistent in style, and consistently formatted?
[x] Are there any uncalled or unneeded procedures or any unreachable code?
[x] Are there any leftover stubs or test routines in the code?
[x] Can any code be replaced by calls to external reusable components or library functions?
[x] Are there any blocks of repeated code that could be condensed into a single procedure?
[x] Are symbolics used rather than “magic number” constants or string constants?
[x] Are any modules excessively complex and should be restructured or split into multiple routines?

Documentation

[x] Is the code clearly and adequately documented with an easy-to-maintain commenting style?
[x] Are all comments consistent with the code?

Variables

[x] Are all variables properly defined with meaningful, consistent, and clear names?
[x] Are there any redundant or unused variables?

Arithmetic Operations

Loops and Branches

[x] Are all loops, branches, and logic constructs complete and correct?
[x] Are all loops, branches, and logic constructs properly nested and avoid unnecessary nesting?
[x] Can any statements that are enclosed within loops be placed outside the loops?

Defensive Programming