build: Replace Autotools with Meson

Quick rundown of benefits:

- Much faster:
  - Autotools (with autogen): 22 seconds
  - Meson: 7 seconds
  - Meson (with ccache): 2 seconds

- Simpler:
  - ~1000 lines smaller
  - Single simple language

- Potentially better Windows (Visual Studio) support

What is not done:

- Complete Windows support
- OSX support (easy)

Closes #2013
Closes #1937
Closes #1803

win32/version-template.ps1

@@ -1,6 +1,6 @@
 param ([string] $templateFilename, [string] $outputFilename)
 
-$versionParts = Select-String -Path "${env:SOLUTIONDIR}configure.ac" -Pattern '^AC_INIT\(\[HexChat\],\[([^]]+)\]\)$' | Select-Object -First 1 | %{ $_.Matches[0].Groups[1].Value.Split('.') }
+$versionParts = Select-String -Path "${env:SOLUTIONDIR}meson.build" -Pattern "  version: '([^']+)',$" | Select-Object -First 1 | %{ $_.Matches[0].Groups[1].Value.Split('.') }
 
 [string[]] $contents = Get-Content $templateFilename -Encoding UTF8 | %{
 	while ($_ -match '^(.*?)<#=(.*?)#>(.*?)$') {