Turn modified fdlibm into Jerry's own libm

* Rename modified fdlibm to jerry-libm
  * Move third-party/fdlibm to jerry-libm
  * Rename original fdlibm.h to jerry-libm-internal.h
    * And remove it from the public headers.
  * Rename jerry-libm's public header to math.h
    * This also makes jerry-core sources include `<math.h>`. Therefore,
      should anyone want to use a different libm implementation with
      jerry, it becomes possible. (The same way as we provide a minimal
      libc with standard headers, but should it be insufficient or
      conflicting for someone, it can be replaced.)
  * Drop `s_` prefix from jerry-libm sources
    * The original fdlibm implementation had various prefixes (e.g., `k_`
      for sources of kernel routines, and `w_` for wrapper routines), but
      after the specialization of fdlibm to jerry, only `s_` remained.
      Since it does not encode anything anymore, it can be dropped.
  * Stylistic edits to jerry-libm's CMakeLists
    * Align project name with other CMakeLists in the code base
  * Move Jerry-LibM under Apache License
    * Using the same approach as was used by linux-wireless when ath5k
      driver license needed clarification. Solution was proposed by SFLC.
      External mail for future reference: http://lwn.net/Articles/247806/

* Tests & checks
  * Remove FD from the name of libm unit test-related files
  * Make vera++ and cppcheck check jerry-libm

* Targets
  * Speculative update of targets to use jerry-libm

JerryScript-DCO-1.0-Signed-off-by: Akos Kiss akiss@inf.u-szeged.hu

targets/esp8266/docs/ESP-PATCHFORJERRYSCRIPT.md

@@ -23,7 +23,7 @@ index caf8e32..dadaceb 100644
 +    _jerry_text_start = ABSOLUTE(.);
 +    *\libjerryentry.a:*(.text*)
 +    *\libjerrycore.a:*(.text*)
-+    *\libfdlibm.a:*(.text*)
++    *\libjerrylibm.a:*(.text*)
 +    _jerry_text_end = ABSOLUTE(.);
 +
 +  } >irom0_0_seg :irom0_0_phdr