Translate chapter2
Finish translation of chapter 2
Update vocabulary
Merge branch 'chapter2' into gh-pages
proof reading of chapter2
s/伝搬/伝播/g
Merge branch 'chapter2_proof_reading' into gh-pages
Halfway of proofreading of chapter2
Merge pull request #10 from delta2323/gh-pages

Translation of chapter2 complete.