Fixed several typos and grammar errors (#821)

docs/programmers/api-variables/variable-compile-id.md

@@ -1,7 +1,7 @@
 \$compile\_id {#variable.compile.id}
 =============
 
-Persistant compile identifier. As an alternative to passing the same
+Persistent compile identifier. As an alternative to passing the same
 `$compile_id` to each and every function call, you can set this
 `$compile_id` and it will be used implicitly thereafter.
 
@@ -10,7 +10,7 @@ post-filters](#plugins.prefilters.postfilters) you must use a unique
 `$compile_id` to keep the compiled template files separated.
 
 For example a [prefilter](#plugins.prefilters.postfilters) that
-localizes your templates (that is: translates language dependend parts)
+localizes your templates (that is: translates language dependent parts)
 at compile time, then you could use the current language as
 `$compile_id` and you will get a set of compiled templates for each
 language you use.

docs/programmers/api-variables/variable-locking-timeout.md

@@ -2,6 +2,6 @@
 ==================
 
 This is maximum time in seconds a cache lock is valid to avoid dead
-locks. The deafult value is 10 seconds.
+locks. The default value is 10 seconds.
 
 See also [`$cache_locking`](#variable.cache.locking)

docs/programmers/api-variables/variable-use-sub-dirs.md

@@ -10,7 +10,7 @@ environments do not allow PHP processes to create directories, so this
 must be disabled which is the default.
 
 Sub directories are more efficient, so use them if you can.
-Theoretically you get much better perfomance on a filesystem with 10
+Theoretically you get much better performance on a filesystem with 10
 directories each having 100 files, than with 1 directory having 1000
 files. This was certainly the case with Solaris 7 (UFS)\... with newer
 filesystems such as ext3 and especially reiserfs, the difference is