Subset included code files by line number

This commit adds support for extracting individually specified lines
from an included file.

It also:
changes the syntax for specifying git tagged file inclusions to
'git: {tag: a_tag}'."

fixes a bug where retrieving a git tagged file would overwrite
the current working copy.
Subset included code files by line number

This commit adds support for extracting individually specified lines
from an included file.

It also:
changes the syntax for specifying git tagged file inclusions to
'git: {tag: a_tag}'."

fixes a bug where retrieving a git tagged file would overwrite
the current working copy.
Merge branch 'include_code_by_line_number' of https://github.com/skmetz/polytexnic into include_code_by_line_number
Merge pull request #104 from skmetz/include_code_by_line_number

Subset included code files by line number