Remove obsolete base integer prefixes

`0` by itself as a prefix for octal needs to be removed as prefix `0`'s
are parsed as decimal numbers now in Elixir 1.0.0+.
Decimal integers
Underscores in decimal integers

Allow '_' between digits, but not the end of the number.
Decimal floats with optional exponents with optional sign
Add Decimal Integers and Floats to README
Update Color Settings screenshot

Include decimal integers and floats
Land #39, Decimal integers and floats
Add decimal integers and floats to changelogs