syntax: php: color also variable names, and color more reserved words

Most of the keywords listed on the following URL are now highlighted:
  http://php.net/manual/en/reserved.keywords.php

Also color single-quoted strings, and require that //-type comments
are preceded by whitespace or are alone on a line.

With-feedback-from: M <taur@mail.com>

syntax/php.nanorc

@@ -7,26 +7,29 @@ comment "//"
 # PHP markings.
 color brightgreen "(<\?(php)?|\?>)"
 
-# Functions.
+# Function names.
 color white "\<[a-z_]*\("
+# Variable names.
+color cyan "\$[a-z_]+"
 
 # Types.
-color green "\<(bool|char|const|double|enum|float|global|int|var)\>"
+color green "\<(array|bool|callable|const|float|global|int|object|static|string|var)\>"
 
-# Structure.
-color brightyellow "\<(class|function|new|private|protected|public|for|foreach|while|do|if|else|elseif|switch|case|default)\>"
+# Directives and structure.
+color brightyellow "\<(abstract|as|class|clone|declare|enddeclare|extends|function|implements|include(_once)?|inst(ance|ead)of|interface|namespace|new|private|protected|public|require(_once)?|trait|use|yield)\>"
+color brightyellow "\<(case|catch|default|do|echo|else(if)?|end(for(each)?|if|switch|while)|final(ly)?|for(each)?|if|print|switch|throw|try|while)\>"
+# Operators.
+color brightyellow "\<(and|or|xor)\>"
 
 # Control flow.
 color magenta "\<(break|continue|goto|return)\>"
 
 # Strings.
-color brightyellow "<[^=       ]*>" ""(\.|[^"])*""
+color brightyellow ""(\.|[^"])*"" "'(\.|[^'])*'"
 
 # Comments.
-color brightblue "//.*"
+color brightblue "(^|[[:space:]]+)//.*"
 color brightblue start="/\*" end="\*/"
-##color blue start="<" end=">"
-##color red "&[^;[:space:]]*;"
 
 # Trailing whitespace.
 color ,green "[[:space:]]+$"