(Issue 494): Enhance warning functionality

[rminsil]

This PR adds warning functionality:

• the script outputs warnings
• more kinds of warnings are detected

I also did some refactoring to make adding warning code cleaner, so it's a big PR (sorry Damien!)

There's two kinds of warnings right now:

• consecutive punctuation characters (ignoring whitespace)
• (false negative) punctuation found in the sentences that doesn't have rules defined for it

Here is an example of some warning output:

7 warnings found
====================================================================================================
line: 1
            0         1         2         3         4         5
            012345678901234567890123456789012345678901234567890123456789
           'Hi there - you! (my -    friend )  How's   it  going ?'
                          ^^^
                          (14,17)
>>> WARNING_CODE: 0
>>> DESCRIPTION: Multiple consecutive punctuation characters (ignoring whitespace) - currently this is not normalized
====================================================================================================
line: 2
            0         1         2         3
            0123456789012345678901234567890123456789
           'Hello, . there ! How , are  things !?'
                 ^^^
                 (5,8)
>>> WARNING_CODE: 0
>>> DESCRIPTION: Multiple consecutive punctuation characters (ignoring whitespace) - currently this is not normalized
====================================================================================================
line: 2
            0         1         2         3
            0123456789012345678901234567890123456789
           'Hello, . there ! How , are  things !?'
                                               ^^
                                               (35,37)
>>> WARNING_CODE: 0
>>> DESCRIPTION: Multiple consecutive punctuation characters (ignoring whitespace) - currently this is not normalized
====================================================================================================
line: 3
            0         1         2         3         4
            01234567890123456789012345678901234567890123456789
           'An arabic 3 ٣. Some angle brackets « and ».'
                                               ^
                                               (35,36)
>>> WARNING_CODE: 1
>>> DESCRIPTION: Character '«' (U+00AB) is not a letter or digit or whitespace and is not listed as punctuation. Potential false negative.
====================================================================================================
line: 3
            0         1         2         3         4
            01234567890123456789012345678901234567890123456789
           'An arabic 3 ٣. Some angle brackets « and ».'
                                                     ^
                                                     (41,42)
>>> WARNING_CODE: 1
>>> DESCRIPTION: Character '»' (U+00BB) is not a letter or digit or whitespace and is not listed as punctuation. Potential false negative.
====================================================================================================
line: 4
            0         1         2         3
            0123456789012345678901234567890123456789
           'Hello,  . there! How are things !?'
                 ^^^^
                 (5,9)
>>> WARNING_CODE: 0
>>> DESCRIPTION: Multiple consecutive punctuation characters (ignoring whitespace) - currently this is not normalized
====================================================================================================
line: 4
            0         1         2         3
            0123456789012345678901234567890123456789
           'Hello,  . there! How are things !?'
                                            ^^
                                            (32,34)
>>> WARNING_CODE: 0
>>> DESCRIPTION: Multiple consecutive punctuation characters (ignoring whitespace) - currently this is not normalized

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This change is