Building the docs highlights missing in files / structual issues.

[kurbeco]

writing output... [100%] troubleshooting
/home/mark/Projects/openenergymonitor/docs/main/electricity-monitoring/ac-power-theory/use-in-north-america.md:567: WARNING: 'myst' cross-reference target not found: '/pv-diversion/mk2/index.html' [myst.xref_missing]
/home/mark/Projects/openenergymonitor/docs/main/electricity-monitoring/ctac/calibration.md:238: WARNING: 'myst' cross-reference target not found: 'files/77DB-06-09.pdf' [myst.xref_missing]
/home/mark/Projects/openenergymonitor/docs/main/electricity-monitoring/ctac/calibration.md:240: WARNING: 'myst' cross-reference target not found: 'files/77DE-06-09.pdf' [myst.xref_missing]
/home/mark/Projects/openenergymonitor/docs/main/emonhub/default-configuration.md:90: WARNING: Pygments lexer name 'test' is not known
/home/mark/Projects/openenergymonitor/docs/main/emonhub/default-configuration.md:102: WARNING: Pygments lexer name 'test' is not known
/home/mark/Projects/openenergymonitor/docs/main/emonhub/default-configuration.md:120: WARNING: Pygments lexer name 'test' is not known
/home/mark/Projects/openenergymonitor/docs/main/emonpi2/install.md:15: WARNING: 'myst' cross-reference target not found: 'voltage_sensors.md' [myst.xref_missing]
/home/mark/Projects/openenergymonitor/docs/main/emonpi2/install.md:34: WARNING: 'myst' cross-reference target not found: 'connecting-via-ethernet' [myst.xref_missing]
/home/mark/Projects/openenergymonitor/docs/main/emonpi2/install.md:34: WARNING: 'myst' cross-reference target not found: 'connecting-via-wifi' [myst.xref_missing]
/home/mark/Projects/openenergymonitor/docs/main/heatpumps/heatloss.md:94: WARNING: 'myst' cross-reference target not found: 'files/midterrace_heatpunk_design_report.pdf' [myst.xref_missing]
/home/mark/Projects/openenergymonitor/docs/main/pv-diversion/background/overload-protection-of-mains-electrical-circuits.md:36: WARNING: 'myst' cross-reference target not found: 'files/BTA41_Triac.pdf' [myst.xref_missing]
/home/mark/Projects/openenergymonitor/docs/main/pv-diversion/mk2/index.md:52: WARNING: 'myst' cross-reference target not found: '../../electricity-monitoring/ctac/index.md' [myst.xref_missing]
/home/mark/Projects/openenergymonitor/docs/main/resources.md:7: WARNING: 'myst' cross-reference target not found: 'emonpi2/index.md' [myst.xref_missing]
/home/mark/Projects/openenergymonitor/docs/main/resources.md:14: WARNING: 'myst' cross-reference target not found: 'emontx5/index.md' [myst.xref_missing]
/home/mark/Projects/openenergymonitor/docs/main/resources.md:21: WARNING: 'myst' cross-reference target not found: 'emontx4/index.md' [myst.xref_missing]
/home/mark/Projects/openenergymonitor/docs/main/resources.md:34: WARNING: 'myst' cross-reference target not found: 'emonpi/index.md' [myst.xref_missing]
/home/mark/Projects/openenergymonitor/docs/main/resources.md:40: WARNING: 'myst' cross-reference target not found: 'emontx3/index.md' [myst.xref_missing]

I'm not yet familiar with the wider doc set (have been looking mainly at emonPi3) so I'm not sure any of these are known or are issues that can be ignored but seemed useful to highlight for review.