fix typo
Merge pull request #114 from k-takata/fix-typo6

fix typo
explain that the variable declared in the condition of the while statemet will be destoryed and constructed each time the condition is evaluated.
Maru -> ten.
Period -> maru.
Added a missing "wo".
Merge pull request #116 from hiroshi-manabe/typo-period

Period -> maru.
Merge pull request #117 from hiroshi-manabe/typo-maru

Maru -> ten.
Merge pull request #118 from hiroshi-manabe/typo-wo

Added a missing "wo".