Convert tests from custom unittest.vim to vim-themis format

- Add .themisrc to set up runtimepath for test helpers
- Add test helper in test/autoload/themis/helper/emmet.vim
- Add test files: html, css, haml, slim, others (xsl/xsd/mustache/scss/jade/pug/jsx)
- Update Makefile to use vim-themis (old target preserved as test-old)
- All 181 test cases from unittest.vim are covered

test/autoload/themis/helper/emmet.vim

@@ -0,0 +1,42 @@
+let s:helper = {}
+
+function! s:helper.setup() abort
+  let g:user_emmet_settings = {'variables': {'indentation': "\t", 'use_selection': 1}}
+  for f in split(globpath(getcwd(), 'autoload/**/*.vim'), "\n")
+    if f =~# 'themis'
+      continue
+    endif
+    silent! exe 'so' f
+  endfor
+  silent! exe 'so' getcwd() . '/plugin/emmet.vim'
+endfunction
+
+function! s:helper.expand_word(query, type) abort
+  return emmet#expandWord(a:query, a:type, 0)
+endfunction
+
+function! s:helper.expand_in_buffer(query, type, result) abort
+  silent! 1new
+  silent! exe 'setlocal ft=' . a:type
+  EmmetInstall
+  let l:key = matchstr(a:query, '.*\$\$\$\$\zs.*\ze\$\$\$\$')
+  if len(l:key) > 0
+    exe printf('let l:key = "%s"', l:key)
+  else
+    let l:key = "\<c-y>,"
+  endif
+  let l:q = substitute(a:query, '\$\$\$\$.*\$\$\$\$', '$$$$', '')
+  call setline(1, split(l:q, "\n"))
+  let l:cmd = "normal gg0/\\$\\$\\$\\$\ri\<del>\<del>\<del>\<del>" . l:key
+  if stridx(a:result, '$$$$') != -1
+    let l:cmd .= '$$$$'
+  endif
+  silent! exe l:cmd
+  let l:res = join(getline(1, line('$')), "\n")
+  silent! bw!
+  return l:res
+endfunction
+
+function! themis#helper#emmet#new(runner) abort
+  return deepcopy(s:helper)
+endfunction