Cargo.toml,README.md: Bump version to 0.4.0

Main features since v0.3.0 include:

- Support for eBPF-to-eBPF function calls with automatic stack frame
  management, including:
  - stack frame context preservation during function calls
  - maximum nesting level of 8 function calls
  - customizable StackUsageCalculator for stack size optimization
  - support in both interpreter and JIT modes
  - assembler and disassembler support for eBPF call instructions

- JIT support in no_std mode - users can now manually provide executable
  memory areas to use JIT without requiring the standard library.

- Replacing single-byte address representation with Range type for
  memory access ranges, to reduce memory overhead for maps storing large
  amounts of data; and using the hashbrown crate for better HashMap
  performance in no_std mode.

- Reduced dependency on libc, obtained by replacing several calls with
  standard library alternatives:
  - Replaced rand() with a simple Wyrand implementation
  - Replaced libc::memcpy with ptr::copy_nonoverlapping
  - Replaced libc memory allocation with std::alloc
  Only mprotect() remains as a libc dependency.

- Bumping cargo edition to 2024

- Dependency updates, including:
  - replacing the deprecated time v0.2 crate with std::time::Instant,
    providing cross-platform monotonic time functionality using only the
    standard library
  - cranelift
  - elf (we were stuck with a very old version because newer versions
    had breaking changes; these changes have now been addressed)

- Various fixes and clean-ups

(These notes were mostly generated from the Git history by Claude Code.)

Signed-off-by: Quentin Monnet <qmo@qmon.net>

Author: qmonnet

Cargo.toml

@@ -2,7 +2,7 @@
 
 # Project metadata
 name = "rbpf"
-version = "0.3.0"
+version = "0.4.0"
 authors = ["Quentin Monnet <qmo@qmon.net>"]
 
 # Additional metadata for packaging

README.md

@@ -52,7 +52,7 @@ file:
 
 ```toml
 [dependencies]
-rbpf = "0.3.0"
+rbpf = "0.4.0"
 ```
 
 You can also use the development version from this GitHub repository. This
@@ -388,7 +388,7 @@ to your `Cargo.toml` file.
 
 ```toml
 [dependencies]
-rbpf = "0.3.0"
+rbpf = "0.4.0"
 elf = "0.0.10"
 ```
 
@@ -581,7 +581,7 @@ enabled-by-default features.
 
 ```toml
 [dependencies]
-rbpf = { version = "0.3.0", default-features = false }
+rbpf = { version = "0.4.0", default-features = false }
 ```
 
 Note that when using this crate in `no_std` environments, the `jit` module