Add readln_helper() in std_llvm_include.ll
Implement Operations.readln()
Test cases for System.readln()
Create System.read() declaration
# This is a combination of 2 commits.
# The first commit's message is:

Add read_helper() in std_llvm_include.ll

# The 2nd commit message will be skipped:

#	into read
Implement Operations.read()
Test cases for System.read()