feat: use azure pipelines instead of travis

[baszalmstra]

For an example of the result see:
https://dev.azure.com/mun-lang/mun/_build/results?buildId=49&view=results

Currently the pipeline checks the code with cargo check, runs cargo test for stable, beta, nightly on Linux, and computes codecoverage.

Both the interface is nicer, and its builds considerably faster than travis.

• Builds & tests on Linux
• Builds & tests on Windows
• Builds & tests on macOS
• Builds Beta&Nightly
• Checks formatting with cargo fmt --check
• Uploads code coverage to codecov
• Update readme badges

[baszalmstra]

Checkout out azure pipelines to support all target platforms

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (master@b3040d4). Click here to learn what that means.
The diff coverage is 23.07%.

@@            Coverage Diff            @@
##             master      #10   +/-   ##
=========================================
  Coverage          ?   49.66%           
=========================================
  Files             ?       91           
  Lines             ?     6055           
  Branches          ?        0           
=========================================
  Hits              ?     3007           
  Misses            ?     3048           
  Partials          ?        0

Impacted Files	Coverage Δ
crates/mun_runtime/src/lib.rs	0% <ø> (ø)
crates/mun_abi/src/autogen.rs	0% <ø> (ø)
crates/mun_codegen/src/lib.rs	100% <ø> (ø)
crates/mun_codegen/src/ir/function.rs	75.82% <ø> (ø)
crates/mun_syntax/src/lib.rs	69.49% <ø> (ø)
crates/mun_codegen/src/code_gen/symbols.rs	0% <0%> (ø)
crates/mun_codegen/src/code_gen/linker.rs	0% <0%> (ø)
crates/mun_target/src/spec.rs	0% <0%> (ø)
crates/mun_syntax/src/tests.rs	87.09% <100%> (ø)
crates/mun_codegen/src/tests.rs	97.56% <100%> (ø)

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