0.10.6

CHANGES:

• Use _WIN32 instead of WIN32, as proposed by @jonahbeckford in #137
• PKG_CONFIG_PATH via cygpath on Window (#150 @MisterDA)
• ocaml-solo5 (formerly ocaml-freestanding) defines ocaml_solo5, use this
  in ifdef (arm only, #152 @hannesm)
• mirag-crypto-rng-mirage test: require mirage-unix >= 5.0.0 (#151 @hannesm)
• use oUnit2 as dependency, instead of oUnit (#149 @MisterDA)
• support mipsel and mips64el compilation (#148 @glondu)
• bugfix: define _POSIX_C_SOURCE in entropy_cpu_stubs.c (otherwise clock_gettime
  is not defined - at least on armhf) (#148 @glondu)
• bugfix: compilation on kfreebsd-* (adding FreeBSD_kernel to ifdef)
  (#148 @glondu)