[travis] Add minimal .travis.yml file

Allow for automated builds via Travis CI (https://travis-ci.org).

Note that the bin-i386-linux build platform is deliberately omitted
since the required linux-libc-dev:i386 package is not on the allowed
packages list for the Travis 14.04 ("trusty") container environment.

Signed-off-by: Michael Brown <mcb30@ipxe.org>

.travis.yml

+dist: trusty
+
+sudo: false
+
+language: c
+
+cache: ccache
+
+compiler:
+  - gcc
+
+addons:
+  apt:
+    packages:
+      - binutils-dev
+      - liblzma-dev
+      - syslinux
+      - genisoimage
+
+env:
+  global:
+    - MAKEFLAGS="-j 4"
+
+script:
+  - make -C src bin/blib.a
+  - make -C src bin/ipxe.pxe
+  - make -C src bin/ipxe.usb
+  - make -C src bin/ipxe.iso
+  - make -C src bin/8086100e.mrom
+  - make -C src bin-x86_64-pcbios/blib.a
+  - make -C src bin-x86_64-pcbios/ipxe.pxe
+  - make -C src bin-x86_64-pcbios/ipxe.usb
+  - make -C src bin-x86_64-pcbios/ipxe.iso
+  - make -C src bin-x86_64-pcbios/8086100e.mrom
+  - make -C src bin-x86_64-efi/blib.a
+  - make -C src bin-x86_64-efi/ipxe.efi
+  - make -C src bin-x86_64-efi/intel.efidrv
+  - make -C src bin-x86_64-efi/intel.efirom
+  - make -C src bin-i386-efi/blib.a
+  - make -C src bin-i386-efi/ipxe.efi
+  - make -C src bin-i386-efi/intel.efidrv
+  - make -C src bin-i386-efi/intel.efirom
+  - make -C src bin-x86_64-linux/blib.a
+  - make -C src bin-x86_64-linux/tap.linux
+  - make -C src bin-x86_64-linux/af_packet.linux