Add distribution statements

[kprussing]

Add macros that will programmatically define the distribution statements. These should be of the form

\newcommand\distribution[4]{
...
}
...
\distribution{<level}{<reason>}{<date>}{<controlling office>}

The replacements for arguments 2-4 should be the same for distributions B-E.

See the DTIC specification from Sept 2018.

[kprussing]

This could additionally at the "technology warning" and "destruction notice" blocks.