Use standard lib methods

[ls1955]

This commit:

• Refactor GeneratorHelp#to_capitalized
• Remove GeneratorHelp#to_snake
• Replace GeneratorHelp#to_snake with String#underscore across test_template.ecr

Associated Issue:
Closes #405

[ls1955]

Hmm... Can't figure out the error within space-age exercise.

[ls1955]

After taking a look around, It might be because we are dealing with int and float in space-age exercise?

num_one = 1000000000.to_s
num_two = 31.69.to_s

to_snake(num_one) # => "_1_0_0_0_0_0_0_0_0_0"
num_one.underscore # => "1000000000"
to_snake(num_two) # => "_3_1_._6_9"
num_two.underscore # => "31.69"