Working from the layout created by naps62 I've gone ahead and modified this layout adding in better mouse support, easier toggles for the symbols layer and other personal tweaks.

This file is meant for use with the QMK keyboard firmware

The original README follows below in it entirety

I wanted a layout that suited my Linux & Vim usage. I also didn't like the lack of efficient access to some of the more common special characters used in programming.

• No MT(mod, kc) keys (modifier when pressed, key when tapped). Those keys work with a global timeout. When a key press is shorter than the timeout, it's considered a tap, otherwise it's a hold. I couldn't find any particular timeout that would work for me. I need to use mods extremely fast, but also want the confort of using them more slowly in other occasions. So I gave up on this feature altogether.
• Direct access to {}[]. When programming, these are used extremely often. I was still getting used to the coder layer, and I prefer the arrows on the home row, so I used the bottom-right keys for this.
• Layer keys everywhere. I either use my little finger or my index finger to go to L1, whichever is more confortable in any given situation. L2 is not used while coding/writing, so I don't need an extremely-optimized access to it.
• Lang key. This is nothing more than Super-Space combo, which in my systems (both Linux & Windows) is the shortcut to change the keyboard language. I'm Portuguese, so I often cycle between US layout for coding, and PT layout for writing.
• Special chars on the right-most column. I only use Ctrl & Shift keys on the left side, so I used the right keys to include some of the more useful special characters as well.

• The = and - signs where nowhere to be found. - was already on the base layer, but it's still useful to have a fully-featured NumPad on the coder layer.

• Better media keys. Why was Play/Pause so far away? And where was Mute? I put all my media keys close to each other, including the missing ones
• Arrow keys on home row. I use vim, so I'm always on my home row. I use this sometimes to get around, but not as often as to need them on the base row. I'm fine with them here
• I don't use mouse keys. They're still set up, and I made some changes as an experiment, but I mostly forgot they exist by now.

Miguel Palhas