Make source blocks more consistent, add small SQL translation table, render ASCII diagrams

[gramian]

• Shell type source blocks all start with $ (Section 3,4,6,7)
• Console source blocks all start with > (Section 3,4,6)
• SQL blocks use all caps commands (Section 3,4,6)
• Prepend database name in console blocks where needed (Section 6)
• Make ASCII diagrams render via ditaa (Section 3)
• Add small table comparing differences of Postgres with ArcadeDB SQL (Section 8)
• Fix https://github.com/ArcadeData/arcadedb-docs/issues/261 (Section 7.3.1)

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[lvca]

Super Christian! This is huge. Thanks again.