Bump to v0.3.4

[CasperWA]

Changes:

• Add description about optimade-python-tools version in OpenAPI spec (Extend OpenAPI/spec description #151, @CasperWA)
• Make it possible to use a non-local MongoDB database (supplying a URI in the config file) (Non Local Mongo #150, @shyamd)
• Update base URLs. Remove /optimade, required base URL is now /optimade/vMAJOR, the optional base URLs, including MINOR and PATCH versions in the URL, are still created.
  The OpenAPI spec now only shows endpoints for a single base URL (/optimade/vMAJOR) (Update base URLs #155, @CasperWA)
  Redirect heroku app link to new base URL (Fix heroku badge #157, @ml-evs)
• Move installation instructions from README.md and CONTRIBUTING.md to INSTALL.md (Move installation instructions #156, @ml-evs)
• Bump some dependency / requirement versions (Bump to v0.3.4 #158, @CasperWA)

[codecov]

Codecov Report

Merging #158 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #158   +/-   ##
=======================================
  Coverage   85.09%   85.09%           
=======================================
  Files          39       39           
  Lines        1845     1845           
=======================================
  Hits         1570     1570           
  Misses        275      275

Flag	Coverage Δ
#unittests	85.09% <ø> (ø)	⬆️

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[ml-evs]

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