Allows for multiple line selections, entry to package settings + more

[avila]

The main reason for the pull request is to allow for exact selection to be sent over to stata. Although this is a behaviour not available when working from stata's default do-file editor, I use it quite a lot and believe to be superior when working in a "exploratory/interactive" mode. The main reasons are. 1) one can more easily send a command and exclude some conditions by leaving it out of the selection (and then send with the conditions for comparison) 2) allows for multiple line selection. a minor, but nice feature, is that I often select full lines with triple mouse clicks. Previously it would also run the "following" line, because sublime defaults to moving the cursor to the next line when you select a full line (via triple clicks). when running with exact selection this is no longer an issue.
In any case, the always_extract_full_line is set to true by default for similarity with stata's default behaviour. If nothing is currently selected, then the whole line under the cursor (and not the whole document, because this is a stupid default behaviour) is sent over to stata.

Other than that, this PR includes the following changes: 1) moves StataLinux entry to Package Settings and adds Key Bindings and Settings entries that lead to those settings files. 2) minor changes to Default (Linux).sublime-keymap

[avila]

i didn't see #1 before, in which you implement the whole line selection as default. In any case, the whole line/partial line is left as an option for the user in this PR.

[acarril]

Thank you for the additions!