Adds Projectionist plugin

Greg Hurrell video: https://www.youtube.com/watch?v=3jDafvUESbs

This allows me to jump between c source, header and test files easily.

It is capable of a lot more than this but I haven't looked into it too
much yet.

.gitmodules

@@ -79,3 +79,6 @@
 [submodule "nvim/.config/nvim/pack/bundle/opt/nvim-treesitter"]
 	path = nvim/.config/nvim/pack/bundle/opt/nvim-treesitter
 	url = https://github.com/nvim-treesitter/nvim-treesitter
+[submodule "nvim/.config/nvim/pack/bundle/opt/vim-projectionist"]
+	path = nvim/.config/nvim/pack/bundle/opt/vim-projectionist
+	url = https://github.com/tpope/vim-projectionist

nvim/.config/nvim/init.vim

@@ -11,6 +11,7 @@ if has('packages')
 	packadd! vim-fugitive
 	packadd! vim-json
 	packadd! vim-less
+	packadd! vim-projectionist
 	packadd! vim-repeat
 	packadd! vim-snippets
 	packadd! vim-surround

nvim/.config/nvim/pack/bundle/opt/vim-projectionist

@@ -0,0 +1 @@
+Subproject commit ddfa49f9ece73aca44d2b45d693e7b58adbf8f8c

nvim/.config/nvim/plugin/projectionist.vim

@@ -0,0 +1,25 @@
+let g:projectionist_heuristics = {
+	\'*': {
+	\	'src/*.c': {
+	\		'alternate': [
+	\			'src/{}.h',
+	\			'tests/{}.test.c'
+	\		],
+	\		'type': 'source'
+	\	},
+	\	'src/*.h': {
+	\		'alternate': [
+	\			'tests/{}.test.c',
+	\			'src/{}.c'
+	\		],
+	\		'type': 'header'
+	\	},
+	\	'tests/*.test.c': {
+	\		'alternate': [
+	\			'src/{}.c',
+	\			'src/{}.h',
+	\		],
+	\		'type': 'test'
+	\	},
+	\ }
+\}