Update bitstring syntax in base.ex
Merge pull request #2528 from alco/base-warnings

Update bitstring syntax in base.ex
Ensure functions in `Kernel.SpecialForms` and `IEx.Helpers` are also auto-completed

Closes #2527
use pure erlang function to judge the erlang version, no shell.
Merge pull request #2530 from qingliangcn/master

use pure erlang function to judge the erlang version, no shell.
Ensure type_to_signature works for all AST variables
Revert "Merge pull request #2530 from qingliangcn/master"

This reverts commit 42875c0b72863aa3f263ad227ffc7c454c001ae6, reversing
changes made to be320880b2231c6933a87fea335612cafbfeea7f.
Updating System.cmd return types
Merge pull request #2531 from jwarwick/system_cmd_type

Updating System.cmd return types
Insert new line after IEx clear message