Testing new accelerometer settings & alternate button layout

More sensitive accelerometer settings #17 , and flipping buttons in the menu #21

Increased motion sensitivity levels

This release increases the sensitivity levels to 0-9, and 0 means that motion sensing is turned off.

Fix issue that can allow soldering mode with screen off.

This is a fix for #19
This fixes the problem case that lets you get from cooling mode to soldering mode without re-setting the OLED back to on state.

Increased sensitivity options

This updates the sensitivity options to have a 1-8 scale instead of pre-set values.
Please remember that sensitivity does not apply until you re-start the iron!

Adding Boost mode

This adds boost mode!
This allows you to change the front key (one near the tip) to become a boost button instead of going to temperature editing when in soldering mode. This allows you to set this button to change the soldering temperature for short periods. For example when soldering a big joint and you want to boost the temperature a bit.

The boost temperature is set in the settings as well.

Improve PID settling and response

This small bugfix improves the PID when run at higher input voltages.
The unit was originally tuned on 12V, which is wildly different to the 19v most people are using.
This looks to improve the response and reduce screen flicker.

Improved update rate modes + Setting descriptions

This release updates the previous display modes, where you can now set both the update speed and also adjust temperature rounding.
This also adds descriptions on the settings menu. Just don't press any buttons for 3 seconds and it will scroll a message remind you what the setting changes. Press any button to continue editing.

Updated Display Modes

This release adds new display modes to the iron. This is under the DISPMD menu

• F - Fast mode, what all the older firmware used
• S - Slow mode, only updates once per second
• R - Rounded mode, only shows temperature to 10C accuracy (rounds off last digits)
• N - None, only shows the heating/cooling symbols. No Temperature display

In the future, the None mode will be tweaked 😄

Fixing menu

Fixes the menu not showing the last item.

Adding shutdown time

• Adds time for unit to shutdown (ie exit sleep)
  Used so that the unit doesn't stay in sleep for extremely long periods of time.