1. Yes.
2. Here is a raw dump of the shortcodes at the bottom of this post. I'll add it to the FAQ when I do the general revision this or next month.
To use them, surround the shortcode in parentheses.
Ex. マージ - (comp) to merge or combine sets of data
3. There is now! See the list below.
'abbr' => 'abbreviation',
'arch' => 'archaism',
'comp' => 'computer',
'suffix' => 'suffix',
'col' => 'colloquialism',
'math' => 'mathematics',
'hon' => 'honorific',
'gram' => 'grammar',
'rare' => 'obscure',
'polite' => 'polite',
'sl' => 'slang',
'hum' => 'humble',
'obsc' => 'obscure',
'derog' => 'derogatory',
'obs' => 'obsolete',
'prefix' => 'prefix',
'honorific' => 'honorific',
'ling' => 'linguistics',
'vulg' => 'vulgar',
'particle' => 'particle',
'pol' => 'polite',
'sens' => 'sensitive',
'mil' => 'military',
'fem' => 'female',
'uk' => 'hiragana only',
'sumo' => "sumo term",
"MA" => "martial arts",
"abbr" => "abbreviation",
"arch" => "archaism",
"ateji" => "ateji (phonetic) reading",
"aux" => "auxiliary",
"aux-v" => "auxiliary verb",
"aux-adj" => "auxiliary adjective",
"Buddh" => "Buddhist",
"chem" => "chemistry",
"chn" => "children's language",
"col" => "colloquialism",
"comp" => "computer",
"conj" => "conjunction",
"cop-da" => "copula",
"ctr" => "counter",
"derog" => "derogatory",
"eK" => "exclusively kanji",
"ek" => "exclusively kana",
"exp" => "expressions (phrases, clauses, etc.)",
"fam" => "familiar language",
"fem" => "female or language",
"food" => "food",
"geom" => "geometry",
"ling" => "linguistics",
"m-sl" => "manga slang",
"male" => "male or language",
"male-sl" => "male slang",
"math" => "mathematics",
"mil" => "military",
"num" => "numeric",
"obs" => "obsolete",
"obsc" => "obscure",
"pn" => "pronoun",
"poet" => "poetical",
"pol" => "polite",
"pref" => "prefix",
"proverb" => "proverb",
"prt" => "particle",
"physics" => "physics",
"quote" => "quotation",
"rare" => "rare",
"sens" => "sensitive",
"sl" => "slang",
"suf" => "suffix",
"unc" => "unclassified",
"kyb" => "Kyoto-ben",
"osb" => "Osaka-ben",
"ksb" => "Kansai-ben",
"ktb" => "Kantou-ben",
"tsb" => "Tosa-ben",
"thb" => "Touhoku-ben",
"tsug" => "Tsugaru-ben",
"kyu" => "Kyuushuu-ben",
"rkb" => "Ryuukyuu-ben",
"nab" => "Nagano-ben",
"hob" => "Hokkaido-ben",
"vt" => "transitive verb",
"vulg" => "vulgar expression or word",
"archit" => "architecture",
"astron" => "astronomy, etc.",
"baseb" => "baseball",
"biol" => "biology",
"bot" => "botany",
"bus" => "business",
"econ" => "economics",
"engr" => "engineering",
"finc" => "finance",
"geol" => "geology, etc.",
"law" => "law, etc.",
"mahj" => "mahjong",
"med" => "medicine, etc.",
"music" => "music",
"Shinto" => "Shinto",
"shogi" => "shogi",
"sports" => "sports",
"sumo" => "sumo",
"zool" => "zoology",
"joc" => "jocular, humorous",
"anat" => "anatomical",
"kata" => "katakana",
