Makefile colorizing improvement: colorize at the beginning of line, handling the '\' symbol and other.

[fadeevab]

1). Colorize when the expression at the beginning of line.
2). Handle '\' at the end of prerequisites (the next line should be colorized as a continuation of previous).
3). Colorize (origin|flavor).
4). Fix colorizing of built-in which stands after a common variable.

[fadeevab]

Note: I tested TextMate JSON version microsoft/vscode#27276 in VS Code (see the images), and then ported that JSON to current XML patch. But unfortunately I didn't test current XML version. So, I really appreciate if anybody can help me with testing of current patch.