Support pylama for python (#2266)

* Add pylama for python
* Consolidate python traceback handling

doc/ale-python.txt

@@ -31,6 +31,7 @@ ALE will look for configuration files with the following filenames. >
   pycodestyle.cfg
   flake8.cfg
   .flake8rc
+  pylama.ini
   Pipfile
   Pipfile.lock
 <
@@ -449,6 +450,60 @@ g:ale_python_pyflakes_auto_pipenv           *g:ale_python_pyflakes_auto_pipenv*
   if true. This is overridden by a manually-set executable.
 
 
+===============================================================================
+pylama                                                      *ale-python-pylama*
+
+g:ale_python_pylama_change_directory     *g:ale_python_pylama_change_directory*
+                                         *b:ale_python_pylama_change_directory*
+  Type: |Number|
+  Default: `1`
+
+  If set to `1`, `pylama` will be run from a detected project root, per
+  |ale-python-root|.  This is useful because `pylama` only searches for
+  configuration files in its current directory and applies file masks using
+  paths relative to its current directory.  This option can be turned off if
+  you want to control the directory in which `pylama` is executed.
+
+
+g:ale_python_pylama_executable                 *g:ale_python_pylama_executable*
+                                               *b:ale_python_pylama_executable*
+  Type: |String|
+  Default: `'pylama'`
+
+  This variable can be changed to modify the executable used for pylama. Set
+  this to `'pipenv'` to invoke `'pipenv` `run` `pylama'`.
+
+
+g:ale_python_pylama_options                       *g:ale_python_pylama_options*
+                                                  *b:ale_python_pylama_options*
+  Type: |String|
+  Default: `''`
+
+  This variable can be changed to add command-line arguments to the pylama
+  invocation.
+
+
+g:ale_python_pylama_use_global                 *g:ale_python_pylama_use_global*
+                                               *b:ale_python_pylama_use_global*
+  Type: |Number|
+  Default: `get(g:, 'ale_use_global_executables', 0)`
+
+  This variable controls whether or not ALE will search for pylama in a
+  virtualenv directory first. If this variable is set to `1`, then ALE will
+  always use |g:ale_python_pylama_executable| for the executable path.
+
+  Both variables can be set with `b:` buffer variables instead.
+
+
+g:ale_python_pylama_auto_pipenv               *g:ale_python_pylama_auto_pipenv*
+                                              *b:ale_python_pylama_auto_pipenv*
+  Type: |Number|
+  Default: `0`
+
+  Detect whether the file is inside a pipenv, and set the executable to `pipenv`
+  if true. This is overridden by a manually-set executable.
+
+
 ===============================================================================
 pylint                                                      *ale-python-pylint*