Merge branch 'release/0.0.47' into develop
src: add instance method 'sum()'
test: add instance method 'sum()' testings
lint: add some files for linting pass
readme: add instance method 'sum()' api
npm: 0.0.47 -> 0.0.48
Merge branch 'release/0.0.48' into develop
Merge branch 'release/0.0.48'
src: abstract instance method 'sum'
src: add instance method 'prod()'
test: add instance method 'prod()' testings
readme: add instance method 'prod()' api

fix a mistake
lint: add some files for linting pass
npm: 0.0.48 -> 0.0.49
Merge branch 'release/0.0.49'