Add support for changes to number literals introduced in Go 1.13

[tohjustin]

Requirements

The updated grammar should support syntax highlighting for the following:

• Binary integer literals: The prefix 0b or 0B indicates a binary integer literal such as 0b1011.
• Octal integer literals: The prefix 0o or 0O indicates an octal integer literal such as 0o660. The existing octal notation indicated by a leading 0 followed by octal digits remains valid.
• Hexadecimal floating point literals The prefix 0x or 0X may now be used to express the mantissa of a floating-point number in hexadecimal format such as 0x1.0p-1021. A hexadecimal floating-point number must always have an exponent, written as the letter p or P followed by an exponent in decimal. The exponent scales the mantissa by 2 to the power of the exponent.
• Imaginary literals: The imaginary suffix i may now be used with any (binary, decimal, hexadecimal) integer or floating-point literal.
• Digit separators: The digits of any number literal may now be separated (grouped) using underscores, such as in 1_000_000, 0b_1010_0110, or 3.1415_9265. An underscore may appear between any two digits or the literal prefix and the first digit.

(taken from Go 1.13 Release Notes)

Description of the Change

All the tree-sitter grammar are manually converted from the EBNF (Extended Backus-Naur Form) expressions for each number literal type found in The Go Programming Language Specification:

• Integer literals
• Floating-point literals
• Imaginary literals

All new test cases added to corpus/expressions.txt are obtained from examples in The Go Programming Language Specification

Playground containing code snippet to test with: https://play.golang.org/p/IuWyvmHjHs0

Alternate Designs

N/A

Benefits

N/A

Possible Drawbacks

N/A

Applicable Issues

Fixes #31
Related atom/language-go#174 (PR: atom/language-go#175)

[maxbrunsfeld]

@tohjustin This is very nice. Thank you very much!

[tohjustin]

Thanks! Glad I could help :)