New option to guess indentation

[schorfES]

Try to guess the correct indentation using the following rules:

The indentation of the current line is correct when:

• the amount of indentations is equal to the previous or
• the amount of indentations is one less than the previous line or
• the amount of indentations is one more than the previous line

The option should be set to false by default. The output of this option should not end in a failed validation

[schorfES]

Added in version 0.6.0 and lintspaces 0.2.0