Introduce nvim namespace: Move files.

Move files from src/ to src/nvim/.
- src/nvim/ becomes the new root dir for nvim executable sources.
- src/libnvim/ is planned to become root dir of the neovim library.

src/nvim/testdir/test53.ok

@@ -0,0 +1,64 @@
+start: foo
+xxxxxxxxxxxx'piep'
+bla bla blah
+out " in ""
+"'" 'blah'yyyyy'buh'
+bla `` b`la
+voo "zzzzzzzzzzzzzzzzzzzzzzzzzzzzsd
+
+<begin>
+-<b>asdf<i></i>asdf</b>-
+-<b></b>-
+-<b>asdfasdf</b>-
+--
+</begin>
+b
+bc
+c
+a
+-1
+0
+0
+1
+2
+-1
+1
+2
+-1
+3
+-1
+3
+3
+3
+-1
+0
+1
+2
+3
+-1
+1
+2
+3
+-1
+SEARCH:
+searchmatch
+abcdx |  | abcdx
+join lines
+zerowidth pattern
+elete first and last char
+ uniquepattern
+my very excellent mongoose just served us nachos
+for (j=0; i<=10; i++)
+
+text
+Y
+--1
+
+--2
+
+--3
+DEPP
+--4
+DEPP
+--5
+end: