Linux-v4.x.x compatibility

This release differs from v1.8.0 by only the following:

• Enhanced README file to discuss the required kernel modules #55
• Compatibility with Linux v4.x.x #58 (thank you @nlydeen)

This fast release/tag is mostly for Archlinux folks (who are, for unknown reasons, my main user base), so that mbpfan-git aur package can be updated (thank you @Yamakaky for maintaining it).
I know, such small changes should have brought to v1.8.1, not v1.9.0. But, compatibility with Linux v4.x.x? Come on! :-)

v1.8.0

Enhanced systemd file #45
Cleaned up Makefile and quicker response to high temperatures when starting #48
Return the control to applesmc when exiting #49
Cleanup of resource when exiting #50
Removal of stale pid file instead of aborting #53 #52

v1.7.0

Jumped to v1.7.0 directly as there was not v1.6.0 formally created.
This version provide several improvements to mbpfan.

With respect to v1.5.0, the following was improved:

• support for coretemp and applesmc when built into kernel instead as modules (#27)
• settings are reload if SIGHUP is detected (#4)
• new tests when make tests (#28)
• respawns forever with upstart (601c1fa) [thank you @pjvds]
• fixed bug that eventually caused defunct processes (#37) [thank you @johnf]
• Support for Macbook pro 7,1, 9,2, and 11,2 and Macbook Air 5,2 has been verified (see README.md for the full list)
• Support for linux-3.15.X and later [#38]