Release version 0.5.2

skip trailing when no decimal separator found

only '-' sign allowed for first input

fix #9 - dissalow input sign after sign

Release version 0.5.1

upgraded react-dom (fix vulnerability issue)

bug fix handle backspace on trailing zero

updated example (use expo 3.2)

ignore example/.expo

Merge pull request #8 from MichaelLambs/master

bring sep back

remove the sep

consoles for delete

fix indentation

to fix NaN bug when adding hitting decimal after action button but before a 0