Allow \limits and \nolimits to be used between or after the super- and subscripts.  Report errors for double super- and subscripts for munderover constructs.  Make \underbrace and \overbrace allow \limits.  Resolves issue #901.
Add minimal support for \hfill (just to handle column alignment in matrices and arrays).  Issue #903.
Make \eqalignno and \leqalignno use mlabeledtr so numbers are positioned properly.  resolves issue #902.
Add font data for spaces from U+2000 to U+200B.  Resolves issue #898.
Make SVG output not include emtpy attributes for unknown characters.  Issue #898 and mathjax/MathJax-node#6.
Add space characters to STIX font data for HTML-CSS output.
Simplify output when SVG output extends beyond the top or bottom of the bounding box (makes the SVG entirely self-contained for MathJax-node output).  Issue mathjax/MathJax-node#18.
For glyphs with empty paths (e.g., space characters), just move the x position by the width of the character.  Resolves mathjax/MathJax-node#3.
Merge branch 'issue901' into develop.  Issue 901.
Merge branch 'issue903' into develop.  Issue #903.
Merge branch 'issue902' into develop. Issue #902.
Merge branch 'issue898' into develop.  Issue #898.
Merge branch 'node-issue18' into develop.  Issue mathjax/MathJax-node#18.
Merge branch 'node-issue3' into develop.  Issue mathjax/MathJax-node#3.