Replace Sphinx with MkDocs

Breaking changes:

• no need for :class: or :term: statements anymore
• Google docstring style from now on

docs/includes/glossary.md

+*[AAA]: Authentication, Authorisation, Accounting
+*[BGP]: Border Gateway Protocol
+*[BSS]: Business Support Systems
+*[CFS]: Customer Facing Service
+*[DCIM]: Datacenter Infrastructure Manager
+*[DHCP]: Dynamic Host Configuration Protocol
+*[DNS]: Domain Name System
+*[DTAP]: Development, Testing, Acceptance, and Production
+*[eBGP]: External BGP
+*[FQDN]: Fully Quantified Domain Name
+*[GA]: Access Port
+*[GAN]: Access Node
+*[GAP]: GÉANT Automation Platform
+*[GOAT]: GÉANT Orchestration and Automation Team
+*[GP]: Physical Port
+*[GSO]: GÉANT Service Orchestrator
+*[GUI]: Graphical User Interface
+*[iBGP]: Internal BGP
+*[IGP]: Internal Gateway Protocol
+*[IFS]: Interface Facing Service
+*[IPAM]: IP Address Management
+*[IS-IS]: Intermediate System to Intermediate System
+*[L3VPN]: Layer 3 VPN
+*[LSO]: Lightweight Service Orchestrator
+*[MPLS]: Multi-Protocol Label Switching
+*[MTTR]: Mean Time To Repair
+*[MTU]: Maximum Transmission Unit
+*[NREN]: National Research and Education Network
+*[OOB]: Out-of-band
+*[OSS]: Operational Support Systems
+*[PoP]: Point of Presence
+*[REST]: Representational State Transfer
+*[RFC]: Request For Comments
+*[SDP]: Service Delivery Point
+*[SNMP]: Simple Network Management Protocol
+*[SOT]: Source Of Truth
+*[TBA]: To be added
+*[UAT]: User Acceptance Testing
+*[VM]: Virtual Machine
+*[WFO]: Workflow Orchestrator