Fix problems with nim check (#404)

* Fix problems with nim check

- Multi file errors are not shown in the same buffer
- Fixes parsing of error type that contain ':'

* Remove redundant fnameescape

ale_linters/nim/nimcheck.vim

@@ -3,6 +3,7 @@
 
 
 function! ale_linters#nim#nimcheck#Handle(buffer, lines) abort
+    let l:buffer_filename = fnamemodify(bufname(a:buffer), ':p:t')
     let l:pattern = '^\(.\+\.nim\)(\(\d\+\), \(\d\+\)) \(.\+\)'
     let l:output = [] 
 
@@ -13,13 +14,22 @@ function! ale_linters#nim#nimcheck#Handle(buffer, lines) abort
             continue
         endif
 
-        let l:buffer = l:match[1] + 0
+        " Only show errors of the current buffer
+        " NOTE: Checking filename only is OK because nim enforces unique
+        "       module names.
+
+        let l:temp_buffer_filename = fnamemodify(l:match[1], ':p:t')
+        if l:buffer_filename !=# '' && l:temp_buffer_filename !=# l:buffer_filename
+            continue
+        endif
+
         let l:line = l:match[2] + 0
         let l:column = l:match[3] + 0
         let l:text = l:match[4]
         let l:type = 'W'
 
-        let l:textmatch = matchlist(l:match[4], '\(.*\):')
+        " Extract error type from message of type 'Error: Some error message'
+        let l:textmatch = matchlist(l:match[4], '^\(.\{-}\): .\+$')
 
         if len(l:textmatch) > 0
             let l:errortype = l:textmatch[1]