travis: Reworking travis setup.

* Move the code into scripts inside .travis directory.
 * Build on multiple compiler versions.

Fixes #442 - Make travis build pass
Fixes #441 - Fix git version information on travis build
Fixes #440 - Make travis cache the iverilog build

.travis/common.sh

@@ -0,0 +1,15 @@
+#! /bin/bash
+
+# Setup the CC / CXX from the matrix config
+eval "${MATRIX_EVAL}"
+
+# Look for location binaries first
+export PATH="$HOME/.local-bin/bin:$PATH"
+
+# OS X specific common setup
+if [[ "$TRAVIS_OS_NAME" == "osx" ]]; then
+	export PATH="/usr/local/opt/ccache/libexec:$PATH"
+fi
+
+# Parallel builds!
+MAKEFLAGS="-j 2"