Add inf-clojure-meta

#### Summary
This commit addresses
clojure-emacs#57 (Add an interactive
command to display a var's metadata) by adding a command to show forms metadata: `inf-clojure-meta`.

`inf-clojure-meta` can be called interactively sends the current form to the inf clojure process and evaluates its metadata. It is useful
for testing.

This command should work with clojure (through lein repl), lumo and planck alike.

#### Test Plan
Manually tested the command using clojure, lumo and planck. I put my cursor on a
form and ran it interactively, it displayed the metadata in the inf buffer.

Author: charignon

CHANGELOG.md

@@ -3,6 +3,7 @@
 ## master (unreleased)
 
 * [#135](https://github.com/clojure-emacs/inf-clojure/pull/135): Improve command sanitation code.
+* [#157](https://github.com/clojure-emacs/inf-clojure/pull/157): Add `inf-clojure-meta`
 
 ## 2.1.0 (2018-01-02)
 

inf-clojure.el

@@ -1099,6 +1099,39 @@ If you are using REPL types, it will pickup the most approapriate
 
 (define-obsolete-variable-alias 'inf-clojure-macroexpand-1-command 'inf-clojure-macroexpand-1-form "2.0.0")
 
+;;; Metadata
+;;; ===================
+(defcustom inf-clojure-meta-format
+  "(clojure.core/meta %s)"
+  "Form to retrieve metadata of another form."
+  :type 'string
+  :safe #'stringp
+  :package-version '(inf-clojure . "2.2.0"))
+
+(defcustom inf-clojure-meta-format-planck
+  "(meta %s)"
+  "Planck form to retrieve metadata of another form."
+  :type 'string
+  :safe #'stringp
+  :package-version '(inf-clojure . "2.2.0"))
+
+(defcustom inf-clojure-meta-format-lumo
+  "(meta %s)"
+  "Lumo form to retrieve metadata of another form."
+  :type 'string
+  :safe #'stringp
+  :package-version '(inf-clojure . "2.2.0"))
+
+(defun inf-clojure-meta-form (proc)
+  "Return the form for retrieving metadata in the Inf-Clojure PROC.
+If you are using REPL types, it will pickup the most appropriate
+`inf-clojure-meta-format` variant."
+  (inf-clojure--sanitize-command
+   (pcase (inf-clojure--set-repl-type proc)
+     (`lumo inf-clojure-meta-format-lumo)
+     (`planck inf-clojure-meta-format-planck)
+     (_ inf-clojure-meta-format))))
+
 ;;; Ancillary functions
 ;;; ===================
 
@@ -1345,6 +1378,15 @@ thing.  See variable `inf-clojure-apropos-form'."
   (let ((proc (inf-clojure-proc)))
     (inf-clojure--send-string proc (format (inf-clojure-apropos-form proc) expr))))
 
+(defun inf-clojure-meta ()
+  "Send a form to the inferior Clojure to show its metadata"
+  (interactive)
+  (let ((proc (inf-clojure-proc))
+        (last-sexp (buffer-substring-no-properties (save-excursion (backward-sexp) (point)) (point))))
+    (inf-clojure--send-string
+     proc
+     (format (inf-clojure-meta-form proc) last-sexp))))
+
 (defun inf-clojure-macroexpand (&optional macro-1)
   "Send a form to the inferior Clojure for macro expansion.
 See variable `inf-clojure-macroexpand-form'.