Fixes library function colors, PHP tag colors and PHP variable colors, Makefile targets

[michaelneu]

I really like your theme, but I think some things were missing, so here's a PR with some suggestions:

• For starters, I missed the highlighted library functions. In Visual Studio some library functions are highlighted in purple, so I added this
• The different background color of an embedded source (e.g. PHP inside HTML) annoyed me as it was really distracting for me (removed it)
• I added colors to the PHP tags in general, so they better fit in with other tags
• When working on a bigger web project you'll notice that the $ in JS is marked as an operator (keyword.operator.js), but PHP variables aren't. I liked the look of it, so I added this for PHP variables too.
• Makefile targets were not highlighted (I set them to be the same color as class definitions)