0.5.1: README: update `ENABLE_SYSTEMD` documentation

• Installation issue hotfix (thanks @xdbob)

0.5

• Added exponential brightness scaling (thanks @Schnilz)
• Support logind dbus APIs (thanks @xdbob, @gicmo)
• Fixed return code in silent mode (thanks @frikiluser)

0.4

• Added a --min-value option to set a minimum allowed value for brightness decreases (thanks @taingra)
• Minor refactoring

0.3.2

Added a manpage, thanks @nbraud, @SirCmpwn

0.3.1

• Fixed build on some older debian systems (specify -lm the correct way)
• Allow device names to be specified by a wildcard (e.g. brightnessctl -d "*capslock")

0.3

Note: this release has some changes in install process. Please review the Makefile for more info.

• Prevented code from using non-standard GNU extensions
• Added a --version flag (@christophgysin)
• Added a info operation (renamed from get, which extracts only the current brightness now) (@hcpl)
• Fixed a rounding error with percentages (@modernrio)
• Added an option to automatically install udev rules (@christophgysin, @Miciah)
• Modified the install process to respect DESTDIR/PREFIX conventions.

0.2.1: Fix logical errors

Fixed several logic errors.

0.2

• Extended documentation (thanks to @Fale)
• Allowed to use sign in prefix (e.g. +5% in addition to 5%+)
• Root privileges are no longer required (write permissions are enough, details are in the README)

Huge thanks to @Miciah for fixing a number of bugs:

• A buffer overflow in cat_with()
• Making saving state work from the first try
• Enforcing additional runtime constraints
• Detalising and expanding error handling

0.1.1_p2

• Licensed to MIT
• Made first found device the default one
• Fixed write on older kernel versions
• Fixed the makefile