This commit adds some cosmetic functionality. The main two
improvements are:
* We'll now pay attention to indentation within existing
sections, and when we write new settings or update
existing ones, we'll match the existing indentation.
* When modifying existing settings, the regex now captures
a greater portion of the original line and preserves it.
Basically, the original whitespacing in the line should
remain intact and only the value should be modified.
This commit makes some minor changes to how we handle removing
settings. In particular, it updates all of the line numbers
of the various 'section' objects to correspond to the new
state of the world based on the removal of a line that appeared
before them.
Also adds one more test related to setting removal.
