Conan

Hello,

It seems that the default profile is mandatory in 2.0, even though the error message implies otherwise.

Environment Details (include every applicable attribute)

• Conan version: 2.0.0a2

Steps to reproduce (Include if Applicable)

• remove default profile
• run conan create --profile=whatever

Logs (Executed commands with output) (Include/Attach if Applicab

The documentation says this "Even though mp-units library does not implement any Linear Algebra types it is generic enough to be used with other Linear Algebra libraries existing on the market.". A set of examples using Eigen would be helpful. Blaze would probably be good too, but personally I don't use it so it's a lower priority for me.

Package and Environment Details (include every applicable attribute)

• Package Name/Version: openssl/1.1.1d
• Operating System+version: Linux CentOS 7.7.1908
• Compiler+version: GCC 7.3.1 (devtoolset-7)
• Docker image: **centos:7.7.190

Add support for require-override

The example in https://docs.conan.io/en/latest/integrations/ci/appveyor.html is invalid (indentation, cmmd). I am new to appveyor. I guess it should be:

version: 1.0.{build}
platform:
  - x64

install:
  - cmd: echo "Downloading conan..."
  - cmd: set PATH=%PATH%;%PYTHON%/Scripts/
  - cmd: pip.exe install conan
  - cmd: conan user # Create the conan data directory
  - cmd: cona