1.Fix: Github Incorrect line number on range. 2.Feature: show line number and control expanding

Fix
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line number range L5-L10 was returning the wrong lines, off by one.

Feature
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When a one liner is provided "somefile.rb<b>#L5</b>" line expanding will apply
The number of lines before or after are configurable, and note that they will override the limit set by MAX_LINES
> LINES_BEFORE = 10
> LINES_AFTER = 10

Expanding behavior is controller via a bitwise flagging.
>EXPAND_ONE_LINER = EXPAND_AFTER|EXPAND_BEFORE 

When **SHOW_LINE_NUMBER** flag is on and line range is provided in the URL,
line numbers will be added to the beginning of each line of code.
<pre>1: code line 1
2: code line 2
3: code line 3
</pre>