Put <hr> around bigint methods for consistency

Author: Sainan

docs/Runtime Environment/Bigint.md

@@ -10,60 +10,71 @@ local bigint = require "pluto:bigint"
 print(new bigint("123")) --> 123
 ```
 
+---
 ### `bigint.tostring`, `__tostring`
 As seen above, the `__tostring` metamethod provides a string representation of the Bigint in decimal.
 
+---
 ### `bigint.hex`
 Provides a hexadecimal representation of the Bigint.
 ```pluto
 local bigint = require "pluto:bigint"
 print(new bigint("420"):hex()) --> 1A4
 ```
 
+---
 ### `bigint.binary`
 Provides a binary representation of the Bigint.
 ```pluto
 local bigint = require "pluto:bigint"
 print(new bigint("420"):binary()) --> 110100100
 ```
 
+---
 ### `bigint.add`, `__add`
 Adds two bigints together. Returns a new bigint.
 
+---
 ### `bigint.sub`, `__sub`
 Performs subtraction on two bigints. Returns a new bigint.
 
+---
 ### `bigint.mul`, `__mul`
 Performs multiplication on two bigints. Returns a new bigint.
 
+---
 ### `bigint.div`
 Performs division on two bigints. Returns two new bigints: quotient and remainder.
 ```pluto
 local bigint = require "pluto:bigint"
 print(new bigint(10):div(new bigint(3))) --> 3    1
 ```
 
+---
 ### `__div`
 Performs division on two bigints. Returns a new bigint with the quotient.
 ```pluto
 local bigint = require "pluto:bigint"
 print(new bigint(10) / new bigint(3)) --> 3
 ```
 
+---
 ### `bigint.mod`, `__mod`
 Performs divison on two bigints. Returns a new bigint with the remainder.
 ```pluto
 local bigint = require "pluto:bigint"
 print(new bigint(10) % new bigint(3)) --> 1
 ```
 
+---
 ### `bigint.pow`, `__pow`
 Performs expontentiation on two bigints. Returns a new bigint.
 ```pluto
 local bigint = require "pluto:bigint"
 print(new bigint(2) ^ new bigint(10)) --> 1024
 ```
 
+---
 ### `bigint.bitlength`
 Returns the position of the most significant set bit as a plain integer.
 ```pluto