add v2/doc/coding-style.md
add v2/doc/coding-style.md

kevinwang/PrairieLearn,mwest1066/PrairieLearn,tbretl/PrairieLearn,parasgithub/PrairieLearn,kevinwang/PrairieLearn,PrairieLearn/PrairieLearnHack,mwest1066/PrairieLearn,mwest1066/PrairieLearn,lotrfan/PrairieLearn,lotrfan/PrairieLearn,mwest1066/PrairieLearn,tbretl/PrairieLearn,kevinwang/PrairieLearn,lotrfan/PrairieLearn,parasgithub/PrairieLearn,lotrfan/PrairieLearn,jakebailey/PrairieLearn,PrairieLearn/PrairieLearnHack,parasgithub/PrairieLearn,PrairieLearn/PrairieLearnHack,lotrfan/PrairieLearn,jakebailey/PrairieLearn,parasgithub/PrairieLearn,rbessick5/PrairieLearn,PrairieLearn/PrairieLearnHack,rbessick5/PrairieLearn,parasgithub/PrairieLearn,kevinwang/PrairieLearn,kevinwang/PrairieLearn,jakebailey/PrairieLearn,tbretl/PrairieLearn,tbretl/PrairieLearn,rbessick5/PrairieLearn,rbessick5/PrairieLearn,tbretl/PrairieLearn,PrairieLearn/PrairieLearnHack,PrairieLearn/PrairieLearnHack,PrairieLearn/PrairieLearnHack,rbessick5/PrairieLearn,lotrfan/PrairieLearn,jakebailey/PrairieLearn,kevinwang/PrairieLearn,PrairieLearn/PrairieLearnHack,mwest1066/PrairieLearn,kevinwang/PrairieLearn,lotrfan/PrairieLearn