First non-trivial commit

Add chrome extension manifest, placeholder sounds, background page to
play sound with placeholder functions, and janky jquery-based addition
of hyperlinks in content script ipa_link.js
Corrects makes hyperlink based on text search
Correctly creates non-trivial hyperlink for trivial regex
Adds non-trivial regex for identifying IPA strings

Regex is 80% of the way there, needs to add 0 or more non-ipa-exclusive
characters to beginning of string