#106: Fix handling of blank, non-empty lines.

Before, lines containing any non-newline character were used to determine
the minimum leading whitespace count. However, for lines containing all
whitespaces, the last whitespace would count as the non-newline character.

Now, lines containing any non-newline, non-whitespace character are used
for determining the count. Also, when trimming lines, any whitespaces up
to the minimum count is trimmed, to trim blank lines with fewer whitespaces.