ZHANG, Ruda January 18, 2020:  Convert math-text words to text only when the math symbols are ASCII only. [e4c945c]
ZHANG, Ruda November 24, 2019:  Add climate econometrics; more edits. [a8291fb]
ZHANG, Ruda December 30, 2018:  Use dollar style math markup. [1b7036c]
Ruda Zhang August 07, 2016:  Replace tab with two spaces. [adaa87b]
Ruda Zhang June 26, 2016:  one sentence per line [e15360a]
Ruda Zhang June 26, 2016:  add category tag to wiki pages [a9b356c]
Ruda Zhang June 26, 2016:  Use internal link for wiki pages. [22daaba]
Ruda Zhang June 26, 2016:  use canonical filename and no internal H1 [eeca8ff]