parser: add some infrastructure for more specific errors

* compiler: change s.line_nr in just one place, so that s.last_nl_pos will be updated in tandem too.

* Cleanup spurious spaces.

* Store ScannerPos info inside the cached tokens.

Use the stored information when errors are encountered.

* Fix #2079 ( cannot use type...in assignment ).

* do not store scannerpos per each token, instead rescan the source once on error to get the position.

* compiler: implement highlighting for errors. Use only line/col info stored in the cached tokens.

* fixing building on windows

* Split can_show_color to _nix and _win files.

vlib/term/can_show_color_nix.v

@@ -0,0 +1,11 @@
+module term
+
+import os
+
+fn C.isatty(int) int
+
+pub fn can_show_color() bool {
+	if os.getenv('TERM') == 'dumb' { return false }
+	if C.isatty(1) != 0 { return true }
+	return false
+}

vlib/term/can_show_color_win.v

@@ -0,0 +1,10 @@
+module term
+
+import os
+
+// TODO: implement proper checking on windows too.
+// For now, just return false by default
+pub fn can_show_color() bool {
+	if os.getenv('TERM') == 'dumb' { return false }
+	return false
+}