Add colored output

Use --no-color to disable colors
Use VALA_COLORS to change colors

E.g. VALA_COLORS = "error=01;31:warning=01;35:note=01;36:caret=01;32:locus=01:quote=01"

Fixes bug 734627.
Check destructor names

Edit: make it an error instead of warning

Fixes bug 655343.
parser: Warn on if/else/lock without body

Fixes bug 682906.
parser: Do not accept "static class"-members instead of ignoring "class"
Add additional checks for main methods

Fixes bug 708391.
Improve error message for virtual/override/abstract class methods