Reorganise modules

[davidcole1340]

Module paths are currently long and convoluted. Can easily be shortened (drop ::php, re-export types from ::types instead of exporting modules).

[vodik]

My though is it's probably best to match PHP's own namespacing rules here to keep things easily findable for anyone who has experience with php-src. The first two snake case segments of PHP functions are probably a good guide for organization. For example:

Random sampling from by current build.rs (note for the following examples I'll omit the crate namespace):

• zend_ce_arithmetic_error -> zend::ce::arithmetic_error
• zend_hash_str_find -> zend::hash::str_find -> though likely best wrapped as zend::hash::HashTable::find
• sapi_activate -> sapi::activate
• php_module_startup -> php::modules::startup
• php_execute_script -> php::execute_script

Useful reports can be done from there (e.g. use ext_php_rs::zend::HashTable or use ext_php_rs::HashTable) and maybe even a prelude.

[davidcole1340]

What do you think of this:

- `ext_php_rs`
  - `bindings` - ffi bindings re-exported from `ext-php-rs-sys` crate
  - `error` - rust error
    - `Error`
    - `Result`
  - `alloc` - allocation related
    - `efree`
    - `emalloc`
    - `ZBox`
  - `rc` - zend reference counting
    - `ZRc`
    - `ZRefcounted`
  - `exceptions` - exception related
    - `PhpException`
    - `PhpResult`
    - `throw/throw_with_code`
  - `binary` - relating to binary packing
    - `Binary`
    - `Pack`
  - `closure` - relating to PHP closures, feature gated
    - `Closure`
  - `args` - argument parsing
    - `Parser`
    - `Arg`
  - `props` - relating to PHP class properties
    - `FieldProp`
    - `Property`
  - `types` - all raw PHP types - in separate modules but re-exported through
    `types`. not including Rust types like `Closure`, `ClassObject` etc.
    - `Zval`
    - `ZHashTable`
    - `ZStr`
    - `ZLong`
    - `ZObject`
    - `ZClassObject`
    - `ZCallable`
  - `conv` - any conversion traits
    - `IntoZval`
    - `FromZval`
    - `IntoZvalDyn`
    - `IntoZendObject`
    - `FromZendObject`
    - `IntoConst`
  - `zend` - raw types relating to zend executor
    - `ExecuteData`
    - `Class`
    - `Module`
    - `Function`
    - `ExecutorGlobals`
    - `ArgInfo`
  - `builders` - builders (primarily for `zend` types)
    - `ClassBuilder`
    - `ModuleBuilder`
    - `FunctionBuilder`
  - `flags` - flags and enums
    - `DataType`
    - `...Flags`
  - `prelude`
    - macros, conversion traits etc. anything used regularly. glob imported.