fix "detachExtInterrupt()" in 'RotEnc.cpp'

v1.1.3

fix 'library.properties'

v1.1.2 : fix function name

fix "detachExiInterrupt()" to "detachExtInterrupt()".

v1.1.1 : fix minor bug

fix library.properties to v1.1.1

v1.1.0 : add external interrupt

Merge pull request #1 from kanitawa/dev_ext_interrupt

add attachExtInterrupt

first release

v1.0.0

translated README_ja.md to README.md in En.