Generate `src/html/entities.cr` automatically #2512

Job	Run time
check_format	1m 27s
deploy_api_docs	0s
x86_64-gnu-test-preview_mt	1m 24s
x86_64-gnu-test (1.7.3)	1s
x86_64-musl-test	22s
x86_64-gnu-test (1.8.2)	1s
x86_64-gnu-test (1.9.2)	1s
x86_64-gnu-test (1.10.1)	17s
x86_64-gnu-test (1.0.0, FLAGS=-Dwithout_ffi USE_PCRE1=true)	1s
x86_64-gnu-test (1.1.1, FLAGS=-Dwithout_ffi USE_PCRE1=true)	1s
x86_64-gnu-test (1.2.2, USE_PCRE1=true)	1s
x86_64-gnu-test (1.3.2, USE_PCRE1=true)	1s
x86_64-gnu-test (1.4.1, USE_PCRE1=true)	1s
x86_64-gnu-test (1.5.1, USE_PCRE1=true)	1s
x86_64-gnu-test (1.6.2, USE_PCRE1=true)	1s
	3m 40s

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