Correctly handle nomaps for e.g. <C-Left>

E.g. make sure that the nomap variable for <C-Left>
is called `g:csv_nomap_c_left` (because `-` is invalid in variable
names.)

Fixes #165

autoload/csv.vim

@@ -2345,6 +2345,7 @@ endfu
 
 fu! csv#Map(map, name, definition, ...) "{{{3
     let keyname = substitute(a:name, '[<>]', '', 'g')
+    let keyname = substitute(a:name, '-', '_', 'g')
     let expr = (exists("a:1") && a:1 == 'expr'  ? '<expr>' : '')
     if !get(g:, "csv_nomap_". tolower(keyname), 0)
         " All mappings are buffer local

doc/ft-csv.txt

@@ -614,9 +614,11 @@ is equival to a single backslash '\', e.g. \K would run the lookup function on
 the word under the cursor and \J would join this line with the previous line.
 
 If you want to prevent the mapping of keys, simply set the global variable
-g:csv_nomap_<key> to 1, e.g. to prevent mapping of <CR> in csv files, put >
+g:csv_nomap_<key> to 1, (remove the special characters `<>` and replace `-` by
+`_`), e.g. to prevent mapping of <CR> and <C-Left> in csv files, put >
 
     let g:csv_nomap_cr = 1
+    let g:csv_nomap_c_left = 1
 <
 into your |.vimrc|. Note, the keyname must be lower case.