Refactored tools structure & conventions for reuse (#685)

1.  All common tools are hosted and managed in
    the tools directory (used for both local development
    and continuous integration)
2.  Each tool comprises a directory, akin to a bundle,
    that encapsulates declarative command-line options,
    configuration files and a run script
3.  A single bootstrap script configures a
    development environment
4.  A lightweight runtime provides a common set of
    convenience functions and variables to all scripts

References #672

.tools/cppcheck/config/avr.xml

@@ -0,0 +1,17 @@
+<?xml version="1"?>
+<platform>
+	<char_bit>8</char_bit>
+	<default-sign>signed</default-sign>
+	<sizeof>
+		<short>2</short>
+		<int>2</int>
+		<long>4</long>
+		<long-long>8</long-long>
+		<float>4</float>
+		<double>4</double>
+		<long-double>8</long-double>
+		<pointer>2</pointer>
+		<size_t>2</size_t>
+		<wchar_t>2</wchar_t>
+	</sizeof>
+</platform>