Adds tinycore kernel and initrd for testing

.gitignore

@@ -1,3 +1,3 @@
-imgs
-xhyve
+cmd/xhyve/imgs/stable*
+cmd/xhyve/xhyve
 vendor

cmd/xhyve/imgs/tinycore.txt

@@ -0,0 +1,9 @@
+These are binaries from
+    http://tinycorelinux.net
+with the following patch applied:
+
+mkdir initrd
+( cd initrd ; zcat ../initrd.gz | sudo cpio -idm )
+sudo sed -i '/^# ttyS0$/s#^..##' initrd/etc/securetty 
+sudo sed -i '/^tty1:/s#tty1#ttyS0#g' initrd/etc/inittab
+( cd initrd ; find | sudo cpio -o -H newc ) | gzip -c > initrd.gz

cmd/xhyve/imgs/userboot.txt

@@ -0,0 +1,8 @@
+userboot.so is the FreeBSD user-mode bootloader
+
+So, this is a bit horrible but it works:
+
+  - userboot is compiled on FreeBSD with '-target x86_64-apple-darwin14' CFLAGS
+  - same for the dependencies of userboot (stand, ficl, zfs)
+  - you have to use the MachO linker set header (include/xhyve/support/linker_set.h)
+  - the resulting object files are linked on OS X with 'clang -dead_strip -shared -o userboot.so *.o *.So'