Adds support for FIX protocol

The FIX protocol is commonly used in the financial industry for moving real time information around. Despite the existence of a standard, each implementation is slightly different, and frequently requires the reading of the raw serialized data, which is simply ASCII key=value pairs, delimited by the ASCII SOH character. 

This highlight.js mode makes raw FIX readable. The tests pass.

The mode treats both ASCII SOH (\u0001) and Unicode "Symbol for SOH" (\u2401) as valid field delimiters. ASCII SOH is a control character, and is often not possible to render visibly in a browser. As such the Symbol for SOH is frequently used by tools wishing to display the delimiter.