v5.1.0

• ADD: \thusetup for cover information setting up in kev-value style, wow!
• Fix: an extra space in head
• Fix: underfull box in head
• Fix: typeset 联合指导教师 properly
• Improve PDF info setup. (avoid \makeatletter in the example)
• Improve: lots of updates for both thuthesis.pdf and main.pdf.
• Improve: simplify gulpfile.js.