Is your feature request related to a problem? Please describe.
Amber has no way to represent integer types. Sometimes we may want to accept type that can be represented as an integer. Here are main pros:

• Not every environment comes with bc installed
• Sometimes some calculations have to be done quickly and so calling bc will only slow things down

Describe the solution you'd like

• Add Int data type
• Numeric value that contains . symbol is a Num
• Numeric value that is an integer is an Int
• Handle as and is operator with Int
• Add arithmetic operations for Int values
• len builtin now returns Int value
• fail statement only accepts Int value
• status returns an Int
• Accessor expression accepts an Int instead of Num
• Ranges now work on Int instead of Num
• Lexical comparison works only on Int arrays
• Update documentation covering Int data type

Describe alternatives you've considered
N/A

Additional context
#70