Upgrade to 0.14.0 and integrate zevem

[gballet]

The primary goal of this PR is to integrate zevem for non-native targets, but it also corrects some of the issues of #42.

TLDR this PR moves the EVMC code to its own file, and then zevem is declared as another file. Depending on the build configuration, either one of these files is declared as the vm module, which is referrenced in all other parts of the codebase. Also, a lib module (TODO: rename this to phant) is created to be referenced from all places in the code. This avoids including files by their relative path, which causes a lot of double-inclusion errors.

Note that cmake doesn't support passing triplets, so we activate zevem on all non-native platforms.

[jsign]

@gballet, the PR is still a draft and there're some red CI. Want me to review anyway as requested, or should I wait until is opened?

[gballet]

Just wait please, indeed there are a few things to get right still.